History Main / ForgottenPhlebotinum

** In several episodes, dead people's intestines smeared on you are enough to enable you to pass by walkers unmolested, which everyone seems to forget immediately afterwards.

* A story arc of ''Manga/AyakashiTriangle'' involves an ayakashi duplicate of Matsuri that no one could tell apart from the original--[[TomatoInTheMirror not even the clone]]. They conclude they're indistinguishable by feeling their spiritual aura and seeing they can both control wind, forgetting the many ways ayakashi and humans were established as fundamentally different--for instance, Hinojiki (who one Matsuri meets shortly after the split) can only [[EnergyAbsorption absorb spells]] created by ayakashi, not humans.

*** Season 2 introduces us to the threat posed by Changelings due to their ability to transform in order to blend in among other Ponies to spy on them or to kidnap them, and were still considered a serious threat all the way into Season 6. However due to an instance of Time Travel, Twilight and Spike both wind up in an AlternateTimeline where the Changelings had overrun Equestria long ago [[LaResistance and a small resistance living within the Everfree Forest is all that's left to oppose Queen Chrysalis.]] This resistance [[AlternateUniverseReedRichardsIsAwesome is led by Zecora]]; who managed to have developed [[GlamourFailure a salve specifically-designed to force any disguised Changeling back into their original form when applied to their skin]], which the members of Zecoras' resistance decorate themselves with to ensure that they aren't being infiltrated by disguised Changelings. Despite having spent a considerable amount of time with Zecora; neither Twilight Sparkle or Spike seemed to bother asking this timelines' Zecora for either the recipe to make the salve or several samples of the salve for them to take back into their own time and reverse-engineer. And after they returned to their actual timeline; they did not bother to ask their own Zecora if she could make this Anti-Changeling Salve that her counterpart had created, [[ApathyKilledTheCat only sharing the story of their travels into alternate timelines with their friends who all treated their escapades like it was some interesting story.]]

** The movies introduce the Genesis device (a form of instant terraforming that may bring people back to life as a side effect), which is so much further advanced than anything the Federation possesses before or since that it might as well be magic. The planet it creates disintegrates within a couple weeks, but surely there would be a way to work the kinks out within the next century, and the research that went into it could at least be applied to other projects, like a handy-dandy anti-Borg weapon. But in ''The Next Generation'' and ''Deep Space Nine'' terraforming is a long and arduous process that yields modest results. Ultimately it's a case of NoPlansNoPrototypeNoBackup; every copy of the schematics is lost and everyone who knows how to make it is dead. Given that the Klingons considered it a treaty-violating potential planet-killing superweapon, there was probably political pressure not to rebuild it.
** ''Series/StarTrekTheOriginalSeries'' was notorious for this.
*** In "Plato's Stepchildren", the Enterprise crew discovers kironide, a [[{{Aesoptinum}} drug that gives people telekinetic powers]]. Why wasn't this made a standard part of the medical kit, even if it is too dangerous to use all the time?
*** The subcutaneous transponder ("Patterns of Force"), which gave the ship the ability to lock onto and beam up the landing party if they were out of contact. Its actual purpose in the plot was to give Kirk and Spock a Cool Escape, rather than pull the whole [[TheGuardsMustBeCrazy trick-the-one-inept-guard bit again]]. Despite the number of times they were separated from their communicators, the thing was never seen before or since. You'd think it would be standard issue.
*** Scalosian water ("Wink of an Eye") gives SuperSpeed (though with a serious risk of dying from injuries that would normally be trivially minor).
*** Spores that can regenerate lost body parts, restore the human body to perfect health and give immunity to radiation ("This Side of Paradise").
*** The episode "The Return of Archons" shows that hand phasers have a wide-beam stun setting that can stun a roomful of people all at once. It shoots a flat beam arc at least ninety degrees wide and has a range of at least twenty meters. Despite the obvious usefulness of such a feature, it is used again exactly ''once'' in an episode of ''Voyager''.
*** "A Piece of the Action" showed the ship's phasers could stun people on the ground and could even exclude the building in the middle of the stun area. Never seen again.
*** In "By Any Other Name" the warp drive is modified by the Kelvans to reach Warp 11 with ease, but this technology is apparently forgotten.
** ''Series/StarTrekTheNextGeneration'' indulged in this far too often.
*** Consider the "dimensional inverter" used in the episode "The High Ground", that could transport things straight through even a Galaxy-class starship's shields (or any other shields) without trouble, but had a cumulative and lethal side effect on people who used it repeatedly. And while that's obviously a sane reason not to use it in normal service, it does ''nothing'' to explain why they didn't use it for, oh, one-way trips by inanimate objects straight through enemy starship shields... objects like armed anti-matter warheads, for example. (Or as a Plan B for when crew members are in danger on the planet but can't be beamed up due to an attack on the ship that requires them to keep their shields up or a NegativeSpaceWedgie that blocks the beam).
*** The episode "Lonely Among Us" shows how the transporter could ''bring the dead back to life!'' While the person's consciousness had been converted into energy by the being that had possessed him, the episode seems to imply that they can always re-materialize a previously saved version of a crew member.
*** The Galaxy class has Saucer Separation capability because the Saucer section contains the civilians, laboratories, families, etc., while the lower section contains the warp drive and primary weapon systems. It allows the civilians to be moved out of harm's way if the ship has to go into a firefight. Saucer separation was used twice in the first season of the show, and once in the season 4 premiere, but after that it was forgotten and only sometimes referred to, just to drop the idea afterwards (it was, however, used in one of the movies). The ''Star Trek: The Next Generation Technical Manual'' explains in a footnote that the writers never forgot about the Saucer Separation capability, and originally intended to use it as a fairly standard maneuver whenever the ship expected to go into trouble. However, what they discovered is that depicting the separation on screen and showing crew moving to the other set just took too much time during the episode to show fully, and not doing so was too jarring of a sudden transition. Hence, they used it sparingly (if at all) for pacing reasons. [[note]]Plus, without the saucer component the stardrive section looks very silly.[[/note]]
*** "Hero Worship" has Geordi connecting the shields to the warp drive, more than doubling their strength. Never mind the other hundred times when this would have been useful.

*** "Who Watches the Watchers" has Troi and Riker implanted with subcutaneous communicators, allowing two-way communication between themselves and the ''Enterprise'', which only the ground team can hear. Naturally, this technology was only ever used ''[[HoldingBackThePhlebotinum four]]'' more times over the course of the entire franchise, despite existing as early as the 22nd Century according to ''Series/StarTrekEnterprise''.

*** An episode had Dr. Pulaski get a mutated virus that aged her. They used a stray hair from her brush and a transporter to restore her to a condition before she contracted the illness. In other words, if you keep a healthy DNA sample, you can restore someone to any age and cure any disease.
*** Using two beams due to interference led to the creation of a second Will Riker, completely by accident. Both were physically identical and had the same memories up until that point. Not only is it capable of cloning a person despite there being no additional mass, but there's the question of who is actually materialized, the original person or a copy?
*** How about Dr. Soong's having spent decades trying to hook Data up with a positronic brain capable of sentient thought, while Geordi did the same thing with one poorly-worded request in the holodeck? Oh, they ''tell'' Moriarty that they'll look into how and why it happened so they can try to figure out a way to let him leave the holodeck... and then promptly forget all about it until he shows up again seasons later. He's understandably unhappy about it.[[note]]Seeing as sapient holograms are in service [[Series/StarTrekVoyager just a few years later]], it looks like someone did look into it. [[UnfortunateImplications And they're given about as many legal rights as a wad of used Kleenex.]][[/note]]
*** The Exocomps from [[Recap/StarTrekTheNextGenerationS6E9TheQualityOfLife "The Quality of Life"]] were non-humanoid robots made of off-the-shelf parts that rapidly improved themselves to the point of sentience. Despite being hugely effective and friendly (one of them performs a HeroicSacrifice to save the heroes), they're never mentioned again. Decades later one of them shows up in ''WesternAnimation/StarTrekLowerDecks'' as a junior officer ([[RidiculouslyHumanRobot with daddy issues]]), the Federation having officially recognized them as a sapient race in the meantime.

*** The easily replicable TR-116 rifle, a projectile weapon capable of shooting through walls thanks to a recent modification the episode's villain had made to it (a combination of x-ray goggles and micro-transporter).

*** There is an entire episode based around a Starfleet unit trapped on a planetary facility being attacked by Jem'Hadar infantry. The Starfleet unit is equipped with nothing but small arms and the Jem'Hadar have no artillery or air support and thus have to make frontal assaults on a fixed position. The episode does reveals that the Jem'Hadar do one trick up their sleeve. Cloaked anti-personnel mines, which are literally all over the Federation base. Which begs the question of why don't they just program the mines to kill everyone in the base by going off at the same time? Those mines also don't show up at any other point, when they would be extremely useful as a hidden surprise upon having to relocate.
** In ''Series/StarTrekVoyager'', the crew conveniently forgot several gadgets that could have gotten them home, or at least closer to it:
*** Q Jr, depowered, retains enough Q knowledge to use the Delta Flyer's [insert TechnoBabble here] to create portals, without any unpleasant StarTrekShake-inducing side-effects that we saw. The crew could have done whatever it was that he did and gotten home via a series of portals, or at least - as was often the case with ''Voyager'''s non-deadly shortcuts - shaved a decade or two off their trip before the AppliedPhlebotinum gave out.
*** In "Threshold", where the otherwise successful test of an experimental transwarp engine turns Janeway and Paris into newts. An imposing side-effect, to be sure, but one which they have cured by episode's end, leaving them in possession of a magic new transportation technology which could get them back to Earth almost immediately, '''and''' a cure for its inevitable side-effect. So rather than using it to return to Earth, or even send a ''message'' back to the Federation (this was before the Federation discovered that ''Voyager'' and her crew had survived), they roll end credits and never mention it again. Even ignoring the lizard-fication, "Threshold" mentions that the experimental shuttle's computers were jam-packed with detailed and helpful navigation aids and maps for the entire sector--which are never mentioned again.

*** Seven of Nine once brought Neelix back from the freakin' dead after ''several hours'' via (what else?) nanoprobes. Apparently, the technology must only work on main cast members. Only that one time...
*** Throughout the series, ''Voyager'' manages to cut a collective ''30-50 years'' off their journey. As the (non-altered) future of the series finale "Endgame" shows, after the crew ignored the Borg temporal node, they supposedly spent the next '''26 years''' merrily skipping along on their way to Earth ''without'' the aid of any of the aforementioned technologies. It's like the crew just gave up and decided to go the traditional way, even though Janeway wouldn't have hesitated to use an advantage if one presented itself.
*** The show often gives a reason ship-board transporters won't work, but they neglect to explain why they can't use the shuttle's independently-powered transporters.
*** Several Borg-focused episodes had them assimilating low-tech worlds just to swell their numbers. What makes it this trope is that cloning technology has been frequently shown in the franchise to be widespread and very cheap (to the point that [[Recap/StarTrekDeepSpaceNineS01E04AManAlone petty criminals from low-tech worlds used it to fake their death]]); if all they need is bodies they can just make some.
*** In ''Film/StarTrekIITheWrathOfKhan'' and the ''Series/StarTrekTheNextGeneration'' episode "The Wounded", it's explained that each Starfleet ship has its own unique [[OverrideCommand prefix code]], which allow another Starfleet ship to access their computer and make commands remotely, thus preventing an enemy who doesn't know it from maintaining control. Curiously, in "Message In A Bottle", when the USS ''Prometheus'' gets stolen by Romulan operatives, none of the Starfleet ships sent out to stop the ''Prometheus'' think about using it.
** ''Series/StarTrekDiscovery''

* In several episodes of ''Series/TheWalkingDead'' dead people's intestines smeared on you are enough to enable you to pass by walkers unmolested, which everyone seems to forget immediately afterwards.
** When Michonne is first introduced, she has two walkers on chains like pets. She says that removing their arms and lower jaw made them non-aggressive AND kept other walkers away. Shouldn't everyone use that? It's not like there are a shortage of walkers.

* In ''Webcomic/SluggyFreelance'', an early StoryArc had Riff and Dr. Schlock work together to build a time machine. After the machine is destroyed by a potato chip (it was balloon based), neither of them ever tries building one again, despite TimeTravel having more DeusExMachina potential than anything else. Though considering how much trouble they get into dealing with {{Alternate Dimension}}s and how big a mess they caused with the last time-travel jaunt, even [[MadScientist Riff]] would hesitate to use it.

*** Additionally, in the play ''Theatre/HarryPotterAndTheCursedChild'', it is revealed that the [[TimeTravel Time Turner]] *can* alter the past, as the villain is nearly successful at using one to bring back Lord Voldemort.

** ComicBook/LexLuthor [[CutLexLuthorACheck invents]] teleporters, time machines, cloaking devices, a gizmo that sucks the GreenLanternRing off its wearer's finger, etc., etc. ... uses them once ... and then then never uses them again, even in situations where one of them would save the Legion of Doom's bacon.

** In ''Literature/HarryPotterAndTheHalfBloodPrince'', the potion 'Felix felices' is introduced- an incredibly powerful ''good luck potion''. It's very rare, and has negative long term effects, but you've got to be a little bit surprised that neither side thought to brew up some for any of the really big/dangerous stuff.

** In one episode, Timmy discovers that mixing Cosmo's sweat into lemonade results in a drink that grants rule free wishes. You'd think after Cosmo had a chance to rest (he was run dry making it) he's use it to solve more problems, but it never comes up.

* ''WesternAnimation/MiraculousLadybug'' does this in the New York Special with the Horse Miraculous that allows the Holder to teleport, which Ladybug should have since she [[spoiler:is the Guardian of the Miracle Box by this point in time.]] So instead of [[spoiler:Wasting time fighting Technolizer, she could've gone back to Paris and fixed the damage in a City without a Hero instead of pinning all the Damage onto Cat Noir.]]

** In the fifth episode, Protect the Pure Heart! A Three-Way Battle, Ami uses her mini supercomputer to track Unazuki's Pure Heart Crystal after it had been stolen from her. Ami doesn't use her supercomputer again after this episode, in spite of how useful it could have been in tracking the Talismans.

** ''Film/IronMan3'' prominently features [[SuperSerum Extremis]], which can heal almost any injury short of [[OffWithHisHead decapitation]] or a [[BoomHeadshot headshot]]. It has the [[SarcasmMode minor drawback]] that it might make you [[SpontaneousHumanCombustion spontaneously explode]], but Tony fixes that issue at the end of the movie, and uses it to remove the shrapnel from his chest. It is never referenced again, even when it could be used to heal [[spoiler: Rhodey]] in ''Civil War'', and he doesn't seem to have any kind of healing factor in any of the other movies.

* The ''VideoGame/StarTrekOnline'' mission "House Pegh" has the eponymous Klingon [[InformedAttribute black-ops team]] in possession of a wide-area cloaking device capable of hiding ships in formation from Iconian sensors. [[SarcasmMode Surely this is a brilliant advance that will change the course of the war!]] (Nope, never mentioned again.)

* ''ComicStrip/CalvinAndHobbes'': Calvin's various cardboard inventions usually only make one or two appearances, even in instances when they would be extremely useful for the situation at hand. In particular, his Cerebral Enhance-O-Tron, which gives him SuperIntelligence, was only used ''once'', where the effects wore off before Calvin could even do anything with his newfound genius, and then never appeared again despite the fact such an invention would be incredibly useful for a BookDumb person like Calvin. Potentially justified because [[MaybeMagicMaybeMundane they might only work in Calvin's imagination]], explaining their inability to be usefulness.

* Every once in awhile this will happen in ''Franchise/KamenRider'' due to the Heisei Series being more toyetic.

** ''Series/KamenRiderKabuto'': Early episodes had ZECT employ thermal cameras which could tell Worms apart from ordinary humans because their SuperSpeed-granting metabolism also raised their body heat. This took away any ability to tell a mystery story, so the cameras were completely forgotten after a few episodes, and some late-game episodes feature ZECT trying to engineer much more convoluted ways of telling Worms apart from humans.

** The loathed ''Comicbook/OneMoreDay'' storyline. Aunt May is dying (well, she's only been in her mid-80's for a few decades now, but she was actually injured). Subverting this trope, Peter scours half the mainstay Marvel cast looking for someone that can heal her. Playing this trope straight, ''[[IdiotPlot nobody can]]''. There's very, VERY thinly implied instances where it's the fact that she's already so old and frail that conventional medicine can't heal her, but considering the fact that those who he approaches include the X-Men (who had no fewer than 3 people at the time whose powers could explicitly heal any wound), {{Reed Richards|IsUseless}}, and Comicbook/DoctorStrange - who is both the Sorcerer Supreme and a former neurosurgeon, there's no reason that SOMEONE couldn't have helped him before he ended up [[DealWithTheDevil letting Mephistopheles wipe out the entire history of his marriage in exchange for Aunt May's life]].

* The ''VideoGame/StarTrekOnline'' mission "House Pegh" has the eponymous Klingon [[InformedAttribute black-ops team]] in possession of a wide-area cloaking device capable of hiding ships in formation from Iconian sensors. [[SarcasmMode Surely this is a brilliant advance that will change the course of the war!]] (Nope, never mentioned again, which amazingly is one of the ''lesser'' reasons the mission is considered an IdiotPlot.)

*** If this sounds like an IdiotPlot, in this case it's usually more of a case of PoorCommunicationKills.

** Certain characters can form lasting {{psychic link}}s with each other, like Gali does with Takua to let him see and record what she witnessess underground. While this ability seemingly has limitations when the plot calls for it, it was only brought up a handful of times and never used when it would have made sense, like when characters split up to explore in a dangerous area.

*** Also, the many, many, '''many''' [[NewPowersAsThePlotDemands one-shot powers displayed by individual Autobots]] that would never be used again. (Most iconically, the PureEnergy [[EpicFlail flail]] and [[AnAxeToGrind axe]] used by Megs and Prime, respectively, in the series premiere only and never again.)

** Averted in ''Literature/HarryPotterAndThePrisonerOfAzkaban''. The [[TimeTravel Time Turner]] is, with only one exception, solely used by [[{{Nerd}} Hermione]] to [[MundaneUtility take multiple classes at the same time]]. However, the perception of this as forgotten phlebotinum is a common fandom mistake: the Time Turner follows the StableTimeLoop model of TimeTravel (you can't actually change the past, only participate in it from a different perspective) and only works in half-hour increments, which isn't that useful.

** The ability to [[FusionDance form a Kaita or a Nui fusion]] has been all but forgotten and had only ever been used a handful of times early on in the series. A Nui fusion last showed up in a 2004 book and willful fusions in general were last referenced in 2006 in the backstories of side characters. The reason is simply that the set designers stopped coming up with Kaita and Nui combinations for figures after 2003, and so the writers chose to ignore them as well, with some official combinations never being used in the story at all. There was ''some'' in-story justification: most characters lacked the training or knowhow to fuse with each pther. [[EarlyInstallmentWeirdness Very early lore]] might have also justified why fusions were rare, as the original two Toa Kaita could only be formed in specifically designed underground chambers after collecting a set of {{MacGuffin}}s, however this idea was ignored in later canon.

** Franchise co-creator Bob Thompson was fond of kooky ideas like having an oddball character called Kapura travel super fast by moving super slow. Since none of the other writers understood this ability, it was never utilized beyond a game mechanic in a 2001 online game.

** In ''Film/IronMan1'', Tony Stark uses a small missile to easily obliterate the military tank that has just knocked him out of the sky. A small magazine of these would be incredibly useful in many situations in future movies, but apparently, he forgets to include them.

** In ''Film/StarTrek2009'', the Spock from an alternate future introduces "transwarp transporting", which works across interstellar distances. He shows this to the younger version of Scotty, and uses it to send him and Kirk to the ''Enterprise'', which is currently traveling at warp speed. In ''Film/StarTrekIntoDarkness'', Harrison uses it to beam from Earth to the Klingon homeworld Qo'noS. This demonstrates that knowledge of the technology ''did'' leak out, but is now exclusively used by the villains, with the heroes seemingly no longer remembering how to do it, even though they were the first to learn how it works.
** ''Film/StarTrekIntoDarkness'': It is revealed late in the film that [[spoiler: an augment's blood can resurrect the dead]], and is subsequently used to heal [[spoiler:Kirk from fatal radiation poisoning (after a point in which everything but his higher brain functions have failed)]]. This is a pretty significant discovery to have lost for two hundred years.

** ''Series/KamenRiderKabuto'' had the ZECT camera which could denote Worms from ordinary humans. That would've been useful later, but instead, characters had to find out who the worm was the hard way. It was completely forgotten after a few episodes.

* The ability of various ''Toys/{{Bionicle}}'' characters to [[FusionDance form a Kaita or a Nui]] has been all but forgotten, and had only ever been used a handful of times early on in the series. This can be attributed to the set designers not coming up with combinations for the later sets, though a couple of already existing combinations still didn't get to be used, even when they would have come in really handy. There is no in-story explanation for this: the writer simply doesn't want to use them.

** In ''Film/IronMan1'', Tony Stark uses a small missile to easily obliterate the military tank that has just knocked him out of the sky. A small magazine of these would be incredibly useful in many situations in future movies, but apparently he forgets to include them. This is lampshaded in many of the ''WebAnimation/HowItShouldHaveEnded'' parodies, where Tony will often shout "Tank Missile!" and easily resolve the conflict.

** ''Website/{{Cracked}}'' wondered [[http://www.cracked.com/article_21025_5-reasons-harry-potter-wizards-are-huge-threat.html wondered why innocent people like Hagrid and Sirius Black had to go to jail]] in a world with truth potions and mind-reading spells.