"No matter how well it would perform, I will never construct any sort of machinery which is completely indestructible except for one small and virtually inaccessible vulnerable spot."Everything has a weakness, every lock has a key, every curse a loophole, and the flaw will come into play to bring down the device. This applies to basically every "immovable object" and "unstoppable force" in fiction, be they objects, characters, science, or magic. The idea is twofold: inside the story, the creator of the device or technique may incorporate a Necessary Drawback that will make it stronger, while the author gives the protagonists (or antagonists) a way to defeat it and maintain suspense and narrative flow by limiting the Deus ex Machina. When justified in a setting, it's usually explained that magic is not free, and the only way to make an unstoppable whatever is to, ironically, build in a weakness that makes it stoppable. Clever creators may even keep the weakness a secret to use in case the machine (or person) should be turned against them. Others may try to make it an Impossible Task. It can be a key to a Tailor-Made Prison, a physical weak point, not being able to harm virgins or the like, or a Curse Escape Clause. If the weakness is a Power Source, Soul Jar, or a form of remote control, destroying the "Keystone" destroys the device/weapon/person/army. See also Celestial Deadline, Necessary Drawback, and Power at a Price. Compare Achilles' Heel, which is this for creatures/characters.
— The Evil Overlord List, Rule 25
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- Nen abilities in Hunter × Hunter can be given a condition and a consequence to boost their power. The more restrictive the condition, and the worse the consequence if they break that condition, the more the technique's power is multiplied by. For instance, Kurapika's "Chain Jail" power has the condition "may only be used on members of the Phantom Troupe", and the consequence "automatic instant death", and as a result is practically unbreakable.
- This trope is played with in Naruto. Every technique, no matter how allegedly perfect it is, has a flaw; be it a simple case of Elemental Rock-Paper-Scissors, an exploitable Red Ring of Death, a loophole that can be used against the user, or one single weakness. Whenever an enemy doesn't say it himself it becomes a plot point to figure this flaw out and using it to the protagonists' advantage.
- The trope is exemplified with The Third Raikage, whoms very body was an Immovable Object and could No-Sell any and all attacks, (save for one unknown attack that left him with a deep scar on his chest; a great shame to him,) and also had an Unstoppable Force in the shape of a Lightning Elemental Finger Poke of Doom. It turns out that the scar was accidentally self-inflicted by his Unstoppable Force technique, thus why it was such a great cause of shame to him, and he is finally brought down by having the attack redirected into his own body. A minor character comments upon the paradox of a warrior owning both an ultimate armor and an ultimate weapon and one of the two would have to be more "ultimate" than the other.
- Another point is the (as explicitly stated by the caster, a perfect technique without drawbacks) "Impure World Resurrection". The zombies are enthralled to the caster, immortal, have infinite chakra and can only be temporarily immobilized by sealing techniques. Once the caster cancels the jutsu for any reason, the zombies are sent back to the afterlife. That is, unless you summon a zombie who knows the same technique. When the effect is dismissed, it's possible for a zombie to re-cast Impure World Resurrection on themselves just before they disappear, causing them to break free from the original summoner's control. This is abused by Madara Uchiha.
- In One Piece, Devil's Fruit is like this. The stuff gives whoever eats it a useful superpower. There's a catch, however: You lose the ability to swim, forever. This is dangerous on a world where seafaring plays such an important role, and pirates who take a chance and use the Fruit are risking their lives.
- Specific powers also have their own weaknesses and/or shortcomings; fighting Logia-type Devil Fruits revolves around this trope more than anything, given their Elemental Shapeshifter powers. Lightning does not work against Luffy's rubber body, forcing the lightning user to exploit his powers' inability to defend against bladed weapons and heat. Wax, even if it is steel-hard, can still melt in a fire...
- The Green Lantern power rings have three. One, each ring must be recharged periodically - it used to be regularly every 24 hours; these days it's treated more like a battery charge where using it more means needing to recharge more often. Two, the rings have no effect on anything that's yellow. And finally, the ring requires thought and concentration to use; if you're tired or distracted, you're useless. The weakness against yellow was originally meant to have been a built-in fail safe in case any one Green Lantern went rogue and tried to use the ring for their own gain. Nowadays it's an unavoidable trait of the green energy the ring wields, though it's something that can be overcome with effort.
- The titular ritual of Revival is only reversible because one of the revivers happened to be pregnant. The undead infant serves as a bridge between worlds and is the only person capable of closing it.
- In Hellboy II: The Golden Army, said army is completely indestructible and invincible. However, its greatest weakness comes from the Golden Crown with which it can be commanded. Disassemble or destroy it and the army becomes a bunch of clockwork paperweights. The Fair Folk tried to counter this by stressing that the crown was completely indestructible. Effective in that nobody ever tried. Until someone did, of course.
- Curses and spells cast by the Big Bad in Disney works generally have an escape clause, although it's rarely stated why they're included.
- The Death Star in Star Wars. A battle station as big as a moon, it was brought down by firing a missile into a small thermal exhaust port, which blew up the entire thing. The weakness the second time around was a little more justified, as the structure was not entirely finished yet.
- Several starships in the Star Wars universe follow design choices that are questionable at best. Take the Nebulon-B frigate: two big dangerous chunks of hull connected by a narrow circular section. Hmm, I wonder where the fighters will concentrate their proton torpedoes? Or the iconic TIE Fighter itself, whose ungainly radiator panels might as well have a target sign painted on them. And unlike the Star Trek universe, where fictional physics dictate the shape of many ships, every other ship in Star Wars proves without a doubt that such construction compromises can be dispensed with by simply utilising a different design.
- The Chronicles of Thomas Covenant.
- The wild magic power of white gold can break the Arch of Time and release Lord Foul from The Land.
- The Arch of Time itself, it prevents Loud Foul from escaping, and limits his power, but if the Creator tried to reach into The Land to stop Lord Foul directly, the Arch would be destroyed and Loud Foul would be released.
- From The Other Wiki: During the Second Chronicles, the thaumaturge Kasreyn said that each of his theurgies contained a single deliberate flaw, because perfection could not endure within the imperfect world. He claimed that white gold would allow him to overcome this.
- In The Dresden Files, we have three Holy Swords. When wielded by a Knight of the Cross such as Michael, and doing God's work, the sword and its wielder is pretty much invincible. However, shedding the blood of an innocent with any of the swords will destroy the sword's abilities. This becomes a plot point in Grave Peril.
- In Life, the Universe and Everything, the population of the planet of Krikkit is in a Slo-Time envelope. However, a separate key (the Wikkit Gate) was first created and then dismantled so that the envelope can be undone after everything else in the universe is dead (so that the Krikkiters can have their wish to be the only things in the universe). Wasn't a problem until they sent out the robots.
- The Lord of the Rings. The One Ring is completely indestructible except for either being thrown into the fires of Mount Doom from whence it came, or dismantled by a smith more skilled than Sauron. note
- The Hobbit. Smaug the dragon is viewed to be nigh-invulnerable by everyone who knows of his existence, including the dragon himself. His scales form a powerful armor in and of themselves, and what would normally be a soft belly is covered by innumerable hard gems embedded in his flesh from years of sleeping atop Dwarven treasure. There's just this one little exposed patch, but you'd need sharp Hobbit eyes to make it out in a dark cavern. And come on, what are the odds of a Hobbit being anywhere near a dragon cave?
- In Terry Pratchett's Sourcery, a wizard's attempt to cheat Death must, by the rules, include a condition under which the contest will end. The wizard in question at first suggests "when Hell freezes over," but is told that this would break a separate rule that forbids living people to be told what the afterlife is like.
- The Demon Prison Zzyzx in the Fablehaven series was constructed according to this principle. If the magicians had attempted to make it utterly inescapable, the magic would have weakened and inevitably failed. By leaving the loophole of the keys, the magic may be kept strong, although the keys must then be defended. Destroying them would result in them reappearing randomly sometime later. To their credit, the architects really did just about everything to make it as hard as possible to successfully unlock the prison.
- In Esther Friesner's Elf Defense, an elf explains that "only the Infinite is infinite" — which means anything not the Infinite has to have a weakness. (Specifically in this case, an elven vulnerability to Latin.)
- In The Book of Swords, Shieldbreaker is the greatest of all the Swords. It can destroy any weapon brought against its wielder. However, it is completely useless against an unarmed opponent, as such an opponent has no weapon to destroy. In the final book, it is also revealed that it cannot destroy Woundhealer, which technically isn't a weapon due to the fact that it can't hurt anyone.
- In the Tales of the Five Hundred Kingdoms series, all curses and such have this. If they don't, the Tradition will put one in.
- Wet Desert: Tracking Down a Terrorist on the Colorado River: While the Glen Canyon Dam could not be brought down by crashing an aircraft into it or a torpedo, a hole and the erosion from the water leaking through said hole could.
Live Action TV
- In Doctor Who, the Sonic Screwdriver can do anything with any device. Unless it's wood or "deadlock sealed". It also doesn't seem to work too well on stone.
- On Knight Rider, the only way to destroy KARR (the Evil KITT) was to shoot him with a laser in the red light under his grill. And Evil Michael had a semi-truck with the same magic protection KITT had, but had a vulnerable spot the size of a quarter.
- In The Vampire Diaries we're told that it's impossible to create a truly immortal being; there always has to be a Kryptonite Factor that will let them die.
- Subverted in the Star Trek: Deep Space Nine episode "Valiant". The cadets crewing the U.S.S. Valiant believe that the Dominion battleship they're planning to attack has a weak spot in its antimatter tanks. They get a clean shot off that causes a spectacular explosion...only to then be blown to scrap because the "weak spot" really wasn't.
- Dungeons & Dragons. In earlier editions, artifacts and relics could only be destroyed by a single specific means. And in Ravenloft, a curse with an escape clause is much more likely to take.
- In fifth edition the Imprisonment spell requires that you stipulate a specific means of breaking the spell when it's cast or it won't work. This allows Dungeon Masters to come up with cunning workarounds to PC castings or to create many a plot hook based on trying to break and older casting.
- The New World of Darkness likes this one.
- Werewolves can make traps etc. for spirits but they always have to include a way out.
- Changeling: The Lost's are taught that everything has a price but nothing is truly forbidden; this comes to the forefront with fetches, some of which have a catch called Fragile Creation in which one specific thing will destroy the fetch utterly - but nothing else will. In most cases, though, Cold Iron will do the trick.
- Furthermore, when a changeling grows in power, his faery nature asserts itself more and more in the form of so-called frailties, supernatural compulsions or weaknesses ranging from needing to count grains of spilled rice to a fatal allergy to mistletoe.
- Things get particularly weird with the True Fae, because conflict and narrative laws are how they force themselves to keep existing at all. Depending on the shape they take, this can make for things like a sentient landscape that will fall apart if you pluck a certain flower, a sword that can't be broken but dissolves when exposed to children's laughter, or a shapeshifting monster that can't hurt people who aren't afraid of it. Battles between True Fae can get decidedly metaphorical; one cut apart another's soul with a well-placed "I love you."
- Vampires gain new powers only if they gain new weaknesses, probably how the whole immortality vs sun thing happened.
- Prometheans can do all kinds of nifty stuff with their bodies, except the power that animates them is utterly unnatural and the universe acts accordingly.
- Mages have phenomenal cosmic power... but are still squishy wizards. They are also loathed by the universe which allows paradox to do nasty things to them.
- Sin-Eaters have it relatively easy though; they get brought back from the dead for the low-low price of a kinda-sorta Enemy Within urging them to indulge in The Dark Side by fulfilling all its old vices, which is often told to shut-it.
- Spirits can gain new powers by taking on a Ban, which can lead to a being that can eat souls but is flummoxed by salt.
- In Exalted, the can holding the Yozis prison is the body of their own king, Malfeas. Their imprisonment was deliberately made imperfect (allowing the lesser Legions to Hell to escape sometimes) for fear of what the Yozis would have done to resist being imprisoned if it had been perfect. (One Yozi's petty and petulant response to imprisonment destroyed roughly 2/3rds to 90% of all reality as it is!)
- The Exalted themselves have perfect defensive charms that can make them invulnerable, but which always come with some sort of situational or tactical flaw. For example, a Solar invulnerability might only work in the presence of someone they care about, or might force them to advance on their most powerful opponent. For Abyssals, their invulnerability might fail in the presence of someone they care about, or force them to flee their strongest foe. For the Infernals, their perfect defenses possess a flaw based on the Yozi patron that grants it. Thus, invulnerability charms granted by Malfeas the Demon City only function in a developed area, while charms from the Ebon Dragon, made from the shadows of everything in existence, cannot defend against holy attacks.
- Though it's touched on in the novels of The Dresden Files, the RPG makes it explicit: If you want Super Toughness, a Healing Factor, or just to be Nigh Invulnerable, you have to have a Kryptonite Factor called "The Catch," which, depending on the availability, gives a discount to powers from those power sets. Having one that's well known and abundant, such as iron to The Fair Folk, gives a bigger discount than one that's obscure or hard to get a hold of.
- The old Champions RPG and the similar GURPS system let you buy a power for X cost, then add modifiers to it. An innate power that couldn't be blocked was the most expensive. An innate power that could be blocked by something rare was less, the more common the blocking agent the cheaper. (Think kryptonite.) A power that was from a focus cost less still, and a power from an obvious focus (the rays shoot out from the jewel set in your forehead) was cheaper, and an obvious, accessable focus (A magic wand that could be stolen from you) even more so.
- Swashbucklers of the 7 Skies allows kolduns to lay hexes, essentially making some use of a magical Gift persistent. The catch is that the koldun has to set a taboo whenever they cast a hex, and if that taboo condition is met then the hex is broken. One of the examples in the book is a koldun cursing someone to be forever followed by the rain so the target may never again enjoy the sun.
- Alexander comments on this trope in King's Quest VI: Heir Today, Gone Tomorrow during the Beast scenario.
- Metal Gear REX from Metal Gear Solid is designed in a way that if the radome dish is destroyed, the otherwise inpenetrable cockpit has to open and expose the very vulnerable pilot otherwise he will be completely blind. Oddly enough this was an intentional design quirk on the part of Hal Emmerich, who felt the machine needed a weakness (along with teeth-shaped metal pieces around the mouth-like cockpit) to "add character".
- Dark Souls: The Primordial Crystal, an extraordinarily powerful magical artifact that Seath the Scaleless studied to obtain his power, and which grants him invincibility... can be shattered with a simple punch. Just because it's powerful doesn't mean it isn't fragile. To Seath's credit, he's clearly aware of this, hiding it behind multiple secret passageways and an army of magical creatures to guard it.
- This is something of a plot point in Umineko: When They Cry. Beatrice explains that, while she could very easily use her magic in ways that leave her utterly invulnerable, it is much more effective to leave the Ushiromiya family a chance (however slim) of successfully defeating her. To illustrate the reasons for this, a comparison is drawn between magic and gambling the greater the "risk", the greater the "reward", so a sure chance of victory leaves nothing to gain. However, it's entirely possible that this isn't meant literally; Bernkastel claims that boredom is the only way to kill a witch, and it's very possible that the "no risk, no reward" paradigm is entirely psychological, as if they leave themselves no chance of losing a game, it is no challenge, and therefore "boring". But given that Beatrice isn't even trying to win in the first place, it's also entirely possible that none of this of this is relevant, or even true, especially after more mundane explanations for anything magical are revealed in the second half of the series.
- According to Word Of God, magic in the Gargoyles universe is more powerful if you give it some sort of get out clause (even an absurd one). Hence the series' premise that the petrification spell on the Gargoyles was undone by the criteria "until the castle rises above the clouds." A regular gimmick on the show. The aforementioned spell is broken in modern times when the castle is moved stone by stone to the top of a skyscraper. Another spell is set to end "when the sky burns" - this condition is met by having robots spread a layer of combustible gas in the atmosphere over the city, then igniting it. Demona and Macbeth have a spell of immortality on them - they will live forever, unless one of them kills the other.
- In Justice League Unlimited, Hephaestus creates an invincible, sentient suit of armor for Ares, but like all his creations, he builds it with one fatal flaw that he keeps secret if it were to be used against him (or possibly because Zeus considers it blasphemous for perfection to exist in anything except gods): the suit is powered by conflict, so if nobody is fighting around it, it shuts down, which may not sound like much of a weakness until, say, someone throws rocks at you from 10 miles distant, too far away to activate the amour. This weakness is removed by Felix Faust when he uses it as his new body. Fortunately Hawkgirl's weapon is the Kryptonite Factor for the suit. Wonder Woman's armor apparently has such a weakness too. When she goes to ask Hephaestus directly how to stop the Annihilator, he refuses to tell her, asking if she would want him to tell people about the weakness he built into her own gear.
- In Shrek Forever After, Shrek's wish to live "for one day as an ogre" does indeed have an escape clause. He must receive true love's first kiss. Too bad Fiona, having had to rescue herself, is now a Badass warrior leading La Résistance and NOT the least bit impressed by Shrek's attempts to court her. And he has literally one day to do it.