History Main / ForbiddenChekhovsGun

* All Black the Necrosword in ''[[ComicBook/TheMightyThor Thor: God of Thunder]]'', the weapon of Gorr the God Butcher. It turned a fairly spindly and starved mortal into [[GodOfEvil an abomination]] that pummelled three different versions of Thor (young Thor, present Thor and Skyfather Thor) into the metaphorical dirt. Unfortunately, it tends to have a rather detrimental effect on the wielder's sanity.

* During the beginning of one episode of ''WesternAnimation/BatmanBeyond'', when Terry asked why Bruce never got to use an experimental, heavily-armored type of Batsuit in the Batcave, Bruce told him that it put a massive strain on his condition. Later in the episode, Terry gets kidnapped by Inque to lure Bruce into a trap. Bruce waltzes right in, and just when Inque believes she's strangling him Bruce breaks out of her grasp and reveals that he was now wearing the armored suit. At the sight of this Terry has an OhCrap, and indeed during the fight operating the suit is taking its toll on the older Batman.

* In ''VideoGame/TheLegendOfZeldaTearsOfTheKingdom'', Mineru speaks to Zelda of draconification - how swallowing a [[AmplifierArtifact secret stone]] turns the imbiber into an immortal dragon, albeit a mindless one. [[spoiler:Zelda, who was trying to find a way to return to her time, dismisses the notion out of hand, as losing her mind would mean she would not recognize anyone in her time, even Link. Later, after Mineru's body is destroyed and Rauru sacrifices his to seal Ganondorf away - after Ganondorf stole Sonia's secret stone to become the Demon King, at that - Zelda receives the Master Sword from the future and realizes that, given her power over sacred light, all she can do for Link is repair the Master Sword until it returns to his hands. And thus, to carry out that deed, she swallows the secret stone in her possession.]]

* At the beginning of the ''ComicBook/{{Supergirl}}'' arc ''ComicBook/RedDaughterOfKrypton'', the [[Franchise/GreenLantern Red Lanterns]] explain to Supergirl that she can never, ever, take her Red Lantern Ring off since she would die. [[spoiler:At the end of the story, Kara removes her ring to try to kill an enemy that was taking over her body. She ends up surviving after being thrown into the sun.]]

* In ''VideoGame/TheLegendOfZeldaTearsOfTheKingdom'', Mineru speaks to Zelda of draconification - how swallowing a secret stone turns the imbiber into an immortal dragon, albeit a mindless one. [[spoiler:Zelda, who thought to find a way to return to her time, dismisses the notion out of hand, as losing her mind would mean she would not recognize anyone in her time, even Link. Later, after Mineru's body is destroyed and Rauru sacrifices his to seal Ganondorf away - after Ganondorf stole Sonia's secret stone to become the Demon King, at that - Zelda receives the Master Sword and realizes that, given her power over sacred light, all she can do for Link is repair the Master Sword until it returns to his hands. And thus, to carry out that deed, she swallows the secret stone in her possession.]]

* The Omega 13 from ''Film/GalaxyQuest''. Somewhat played with. None of the characters even ''know'' what it does, including the aliens who built it. So they don't want to use it, because they don't know what it will do. This is because it was only mentioned before the [[AliensStealCable cliff-hanger ending of the two-part episode that was never finished when the show was canceled]]. They eventually gamble on a fan's theory that it [[spoiler:undoes whatever went wrong in the past 13 seconds, which turns out to be correct]].

* In ''[[https://www.fanfiction.net/s/11898648/22/Harry-Potter-and-the-Rune-Stone-Path Harry Potter and the Rune Stone Path]]'' Bathsheda Babbling tells Harry to ''never ever'' even ''try'' to attempt an Animagus ritual which was made illegal due to the danger of dying or being stuck in your animal form forever. Guess what he ends up using to help him escape from a chimera in a souped-up version of the Triwizard Tournament...
* Played for laughs in ''Theatre/AVeryPotterMusical'' in which Harry shouts: "don't cross the streams!" when the [[PowerTrio trio]] summon their Patronus. And Malfoy. But the dialogue the Ghostbusters use is used in AVPM as well, though to dicuss why Harry has to compete in the House Cup tournament rather than beam-crossing.

* ''LightNovel/{{Slayers}}'' offers another example with the Giga Slave. In order to keep it from being Lina's answer to every problem, a GodzillaThreshold aspect was introduced. Lina learns that the spell could cause the world to turn to chaos, and vows to never use it again; naturally, she's forced to do so at the end of Slayers Next.

* In the first ''VideoGame/ShadowHearts'' game, all characters have a Sanity stat during battle. If this reaches zero, the character goes berserk, attacks their allies, and will not gain experience if you win the battle. The strategy in many difficult battles involves keeping this stat up while various effects suck it away. How does one unleash the final, most powerful transformations of the main character? By leveling the transformations up to max and then going insane while fighting in them. Something of a GuideDangIt.

* At the beginning of the ''Comicbook/{{Supergirl}}'' arc ''ComicBook/RedDaughterOfKrypton'', the [[Franchise/GreenLantern Red Lanterns]] explain to Supergirl that she can never, ever, take her Red Lantern Ring off since she would die. [[spoiler:At the end of the story, Kara removes her ring to try to kill an enemy that was taking over her body. She ends up surviving after being thrown into the sun.]]

* In ''Radio/TheHitchhikersGuideToTheGalaxy'', it's generally a really bad idea to activate the Infinite Improbability Drive on the starship ''[[CoolShip Heart of Gold]]'' without proper programming, as '''anything''' could happen as a result. However, when confronted with imminent destruction by a pair of nuclear missiles, [[UnfazedEveryman Arthur Dent]] goes ahead and does it anyway, since [[GodzillaThreshold almost anything else would be an improvement]]. Luckily, the only thing that happens this time is a redecorating of the ship's bridge, and the two nuclear missiles being replaced by a live sperm whale and a bowl of petunias. (Also occurs in the book, TV series and movie adaptations.)

[[folder:Web Comics]]

* ''WesternAnimation/JohnnyTest'': -Johnny teams up with some villains to save the Earth, and they're told right before they head out to not use their powers while holding hands, since it could multiply their powers by 500% or something. Naturally, when their plans are thwarted, they turn to this. It ''sounded'' like the villains refused to do this, and Johnny teamed up with his... dog.

** ''Literature/DeadBeat'': Harry broke the Fifth Law of Magic when he reanimated [[EverythingsBetterWithDinosaurs Sue]]. His necromancy falls into a loophole and he is not prosecuted for it by the council since he did not use it on a human but it colors the council's opinion of him going forward.

* ''Wiki/SCPFoundation'' has combining the two major NothingIsScarier SCPS: SCP-055 (the one where you can only remember what it ''isn't'') and SCP-579 (the one whose entire page is redacted). Their effects on each other are only ever described as "[[ArcWords can't fit round pegs in square holes]]", but it's been used twice; once when aliens conquered Earth and once when the Foundation tried to destroy humanity. In both cases it acted as a ResetButton.

* In ''WesternAnimation/OverTheHedge'', characters tell Hammy not to drink caffeine, it could be dangerous to him, as he's already hyperactive. Later, they tell him to drink caffeine to go into CaffeineBulletTime mode.

* About a third of the way into ''Film/FantasticFour2005'' when the Four are running tests on their capabilities, Johnny gets so hot he melts the walls of the test chamber. Reed stops the test with fire retardant foam, then explains to him that he'd gotten [[SciFiWritersHaveNoSenseOfScale almost as hot as a supernova]] and that this was bad. [[spoiler:During the fight with Dr. Doom at the climax, Reed tells Johnny to go supernova inside Sue's forcefield to try and melt Doom.]]

* In ''[[Webcomic/TheInexplicableAdventuresOfBob The Inexplicable Adventures of Bob,]]'' from the moment Galatea learns about the [[GodzillaThreshold insanely dangerous]] forbidden Nemesite super weapon, the "Butterfly of Iron," it's pretty much inevitable that she's going to find and activate it. When she does find it, she hesitates for a moment until her companion tells her from offscreen, "It is forbidden!" She shoot him a dirty look and pokes the button out of spite. HilarityEnsues.

[[folder:Real Life]]
* The Manhattan Project. Scientists did experiments seeing how close they could get radioactive cores to going critical without ''actually'' making them go critical. They called this [[TemptingFate Tickling The Dragon's Tail]], and considered it a necessary but insanely dangerous thing to do. One core did accidentally go critical (very briefly) on two separate occasions, resulting in the deaths of two researchers and less severe cases of radiation poisoning for several others. They dubbed this one the [[NamesToRunAwayFromReallyFast Demon Core]]. And of course, there are two cases where they [[NukeEm very intentionally let the cores go critical]], but that was the point. There was some speculation that the detonation of the first thermonuclear device ''could'' cause atmospheric nitrogen to start fusing, which would have made our solar system a binary star, briefly. Preliminary calculations indicated it was a long shot but didn't rule it out completely. The probability was deemed high enough that they actually got someone to do the detailed calculations to prove it wouldn't happen.
* Creating the Higgs Boson, a.k.a "the God particle" using the Large Hadron Collider was thought by pop culture to be an easy way to bring about TheEndOfTheWorldAsWeKnowIt and was the subject of quite a lot of controversy at the time. The Collider was activated on schedule regardless, and the Higgs boson's existence confirmed some years later, and if it destroyed the universe, no one has noticed.
[[/folder]]

* The Omega 13 from ''Film/GalaxyQuest''. Somewhat played with. None of the characters even ''know'' what it does, including the aliens who built it. So they don't want to use it, because they don't know what it will do. The reason nobody knows what it does as it was only mentioned before the [[AliensStealCable cliff-hanger ending of the two-part episode that was never finished when the show was canceled]].
* ''Film/{{Ghostbusters|1984}}'' has the iconic warning "Don't cross the streams," which they inevitably have to do at the end of the movie. As former TropeNamer, it was also causing confusion, since this overlaps with GodzillaThreshold. In this case, the non-disaster when they do end up crossing the streams makes internal sense: they are firing into a [[spoiler:ParallelUniverse EldritchLocation where a dark god trying to destroy the world is based, and presumably, [[InferredHolocaust the disaster Egon predicts happens]] '''[[InferredHolocaust there]]''' - and closes the gate]].
** In the [[Film/Ghostbusters2016 2016 remake]], Jillian tells the gang not to shoot the Ecto-1 after Slimer steals it incase the reactor explodes. They end up doing this on purpose at the end to ReverseThePolarity of the HellGate to make it suck all the ghosts back in.
* The [[SuperPrototype Gunstar's]] [[SpinAttack Death Blossom]] attack in ''Film/TheLastStarfighter''; not so much that's it's insanely overpowered (although it is) as that it's never been tested before and might possibly ''blow up their ship''.
* In the ''Film/LostInSpace'' film, ships have hyperspace engines, but it is not a good idea to jump without coordinates or a jump gate as [[BlindJump the exit vector would be random]]. The crew does this anyway when the ship is sabotaged and crashing into the sun. [[spoiler:And ''again'' at the end of the film when the planet they crash-land on turns into a black hole; [[AndTheAdventureContinues it's not revealed where they end up]].]]
* Agent J in ''Film/MenInBlack'' is told by Agent K to never, ever touch the red button inside their car. When the two need to get across the city in a hurry and the tunnel is jammed, he is at last told to push the button -- transforming the car into a high-speed rocket that drives along the ceiling of the tunnel.

'''Banner:''' That's my secret Captain. I'm always angry.\\

** During the TrainingMontage in ''Film/AntMan1'', Hank warns Scott not to tamper with the shrink suit's regulator. Doing so would risk Scott going subatomic and effectively disappear. [[spoiler:Scott eventually does so as an intended HeroicSacrifice to slip past Yellow Jacket's titanium plating to destroy his suit]].
* ''Film/TheFastAndTheFurious2001'': The Dodge Charger in Dom's garage belonged to his father and nobody, not even Dom, dares drive it... until the last ten minutes of the film.

* In ''Film/TheRundown'', Beck refuses to use guns because "bad things happen" when he does. In the final showdown he realises [[BatmanGrabsAGun he has no choice]], and bad things do happen...to countless mooks.

* In ''Franchise/{{Pokemon}}'' - [[TakingYouWithMe Perish Song.]] Especially if you're in a double battle.

* In [[https://tvtropes.org/pmwiki/pmwiki.php/Series/BetterCallSaul Better Call Saul]], the second season premiere is titled "Switch." This refers to a switch Jimmy sees in his office with a taped sign that reads "Do NOT turn OFF!" At the end of the episode, he peels back the tape and switches it. Nothing happens. He switches it back and puts the tape back on.