History Main / LogicalWeakness

* ''Fanfic/RainCodeNewGamePlus'': Aphex and [[SuperHearing Pucci]] can detect living people with their Fortes within a 50- and 500-meter radius respectively. [[spoiler:The hitman posing as Zilch has to exploit their weaknesses in order to put his contingency plan in motion, knowing that they'll be using their Fortes to check on everyone's status on the train occasionally. The hitman first lures Aphex into a room to drug him since he knows that Aphex's [[PsychicRadar Life Detection]] is pinpoint accurate but does not kill him since he knows that Pucci will sense through her [[SuperHearing Audial Aptitude Forte]] that someone has been killed. After the hitman returns the unconscious Aphex to his room, he is able to fake his own death by leaving the real Zilch's corpse in Car 2, set the room ablaze so the body will be burned beyond recognition, and go onto Car 1 and detach it from rest of the train before going on a separate track. Since the train everyone else is on went into a tunnel far enough away from the still moving Car 1, Pucci is unable to hear the hitman's heartbeat with her Forte. It's only when Car 1 attaches to the back of the train that Pucci and Aphex are able to detect his presence, but since they believe "Zilch" is dead, they are unable to identify the sixth individual that just appeared on the train.]]

This premise centers around being consistent with a combination of [[SurprisinglyRealisticOutcome real world logistics intersecting]] with [[MagicAIsMagicA well-developed but entirely fictional science, magic or technology]]. It doesn't always mean the application of the weakness is realistic, only that it does work in the boundaries set up by the setting.

** Rick Shades' epithet relies on being friends with others to work. As such, if he is without any friends, like he is at the start of ''Prison of Plastic'', then he's no stronger than a typical mundie. Likewise, if he loses someone's friendship, he loses the power said friend gives him as well.

** Later in the series, Rainbows Dash gains SuperSpeed. In "Holidays Unwrapped", she mentions she learned the hard way that speed and icy sidewalks are [[TooFastToStop a bad combination]]. She also naturally needs to be free of her movements to reach Super Speed, and an ImpracticallyFancyOutfit hampering her legs can slow her down considerably.

* ''Myth/ClassicalMythology'': Achilles was invulnerable except for his AchillesHeel, but he still needed to breathe. In one story, he got into a fight with the river god Scamander, and Scamander almost managed to kill him by drowning him. Hephaestus had to rescue Achilles.

* In ''Fanfic/CoOpMode'', Taylor needs time to replenish her swarms in between difficult battles, as in canon, but due to her choosing to [[ForWantOfANail become Lady Bug]], she also needs it to repair her more intricate equipment.

* In ''FanFic/WormMoreThanMeetsTheEye'', [[ForWantOfANail circumstances]] mean that Coil brings the hammer down harder on Lisa/Tattletale by demonstrating that he knows all the plans she's been making to get out from under him. While Lisa doesn't know ''how'' he's doing this (essentially, his power allows him to torture it out of her and then make it so that the torture didn't happen, but he retains the information), she realizes that while he'll know about her plans no matter how carefully she makes them, this only works for things she plans out in advance -- if she immediately acts on an idea (in this case, giving herself up to Dragon) instead of setting up a plan, she won't give him the time to learn anything.

** ''Film/Terminator2JudgmentDay'': The [[Characters/TerminatorMainContinuityMachines T-1000]]'s body can take only a single whole shape, which means, as the T-800 2.4 explains, he can't morph his arms into something with mobile parts (like a gun or ArmCannon) or anything with chemicals or complicated moving parts like an explosive. His liquid metal form also lets him re-form after sustaining damage, but being flexible liquid means he [[MadeOfPlasticine is MORE affected]] by gunshots than the solid-frame T-800[[note]]the bullets spread the liquid metal away from the T-1000, and he has to wait for it to slowly rejoin his main mass; in contrast, the T-800 just takes the hit and likely has the bullet bounce off with no damage[[/note]]. It can also only replicate objects of equal size, meaning it can't disguise itself as an inanimate object or something small enough to go unnoticed and sneak up on John.

** In ''Film/ManOfSteel'', Clark initially struggles to adapt to having supersenses, since he needs to learn to filter out being able to hear pretty much everything. This is later used against the other Kryptonians, who suffer the same problem when first exposed to the Earth's atmosphere.

* Chaosbringer in the "Into the Chaosverse" mini-chapter from [[https://www.fanfiction.net/s/13501363/1/Chaos-Effect Chaos Effect]] uses this to defeat All For One. Knowing he has to touch someone to steal their quirk and that All For One's first instinct will be to touch him he decks himself out in a full body suit covered with microneedles that inject a blood cloating chemical into All For One's body. Because any healing quirk All For One has will only attack things not native to All For One's body he begins to have multiple heart attacks and strokes, leaving him a crippled mess for Chaosbringer to kill.

* Several ''Manga/MyHeroAcademia'' stories make it clear that a Quirk that allows someone to copy or negate one Quirk will only affect a single Quirk when used on someone who has multiple ones. (For Aizawa, this is an example of AdaptationalWimp, as in canon he can erase any number of Quirks as long as he can see their users and specifically does nullify all Quirks his target possesses.)
** In ''Fanfic/YesterdayUponTheStair'', Aizawa erases Izuku's Quirk during the quirk assessment test and unknowingly erases his original Quirk (seeing ghosts), not One For All.
** Aizawa again in ''Fanfic/QuirkSequencer'' erases Izuku's Quirk just as he throws his baseball but only erases [[SuperToughness Calcium Reinforcement]], causing Izuku to break his arm while still launching his ball several hundred meters.
** Monoma in ''Fanfic/FromMuddyWaters'' copies Izuku's Quirk but only gets his original quirk, All For One, rather than the dozens of other Quirks that he uses in combat.

* In ''WesternAnimation/Shrek2'', Mongo (an 80-foot-tall Gingerbread Man) is vulnerable to becoming soggy. Natrually, he's defeated with huge pitchers of warm milk.

** [[http://scp-wiki.wikidot.com/scp-661 SCP-661 ("Salesman, Too Good to Be True")]]. He has a CompellingVoice that will make people believe anything he says. However, it was shown that if someone has something they consider more important than listening to him, they can ignore SCP-661's commands. Alternatively, since SCP-661 can only speak English, the Foundation keeps him contained by just hiring people to guard him that don't speak English.

* ''[[https://archiveofourown.org/works/29573091/chapters/72683475 Prophetic]]'': Izuku's Quirk alerts him to what's happening that day via a poem when he wakes up in the morning. However, it has multiple weaknesses. First, Izuku's Quirk only works once a day and only for that day up to midnight. So he can't learn about anything that happens further out. Second, his Quirk's cooldown only resets if Izuku is asleep before midnight, otherwise he won't get a poem that day. Third, unless Izuku focuses on a specific person, the poem will only pertain to those he can travel to on his own[[note]]When Izuku first got his Quirk, it wouldn't alert him to anything more than a few apartments away because his mother didn't let him go further than that. By the time he's a teenager, it will alert Izuku to anything in Mustafu[[/note]]. Finally, the poems can only be so long, which will cause them to prioritize more immediate problems[[note]]Izuku doesn't learn his mother abandoned him until several days afterwards because his Quirk was focusing on things like the USJ attack[[/note]].