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[[quoteright:210:[[Webcomic/BugMartini http://static.tvtropes.org/pmwiki/pub/images/windex_in_doomsday_rocket_8134.png]]]]

->''"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools."''
--> -- '''Creator/DouglasAdams''', ''Literature/MostlyHarmless''

Whether it's TheDitz, TheFool, InspectorOblivious, or a [[EverythingsBetterWithMonkeys monkey]], this miscreant is capable of derailing the most ironclad {{plan}} by unknowingly [[TakeAThirdOption taking a third option]]. They ruin the implausible {{Gambit Roulette}}s by [[FlawExploitation exploiting their one, intrinsic flaw:]] their reliance on {{Contrived Coincidence}}s, [[ClockKing rigid patterns]], and the assumption that nobody would be stupid enough to actually push the BigRedButton or fight the ''apparently'' [[NighInvulnerability unstoppable]] robot.

How can they [[BeatThemAtTheirOwnGame outdo the master at his own game]] with nothing but stupidity and clumsiness? It's precisely '''because''' these characters are the [[ScrewDestiny fools]] and [[YouCantFightFate tools]] of fate that they are uniquely placed to derail these schemes with the gentleness of a [[ButterflyOfDoom butterfly flapping its wings...]][[DoomyDoomsOfDoom of doom!]]

Put another way, they are an author's walking {{deconstruct|edTrope}}ion or LampshadeHanging of the TheoryOfNarrativeCausality: just as easily as a plot can come together [[DidntSeeThatComing it can be pulled apart with the tiniest, most ridiculous things.]]

These characters are TheChessmaster, SmugSnake, ManipulativeBastard, and MagnificentBastard's worst nightmare.

When the character ruins the protagonists' plans by unknowingly doing something small but crucial, he becomes an UnwittingInstigatorOfDoom. When the Spanner can trigger a series of coincidences, it's DisasterDominoes. When the plan is screwed and the character is also aware that he will screw the plan, and doesn't care, he becomes a LeeroyJenkins. Occasionally, may be MistakenForBadass. If the focus isn't on them, they're often an UnknownCharacter.

Compare FinaglesLaw, ItBeganWithATwistOfFate, NiceJobFixingItVillain, OutsideContextVillain, RememberedTooLate.

Opposite of the UnwittingPawn, often ''is'' the UnwittingPawn until the final crucial moment. This is the main cause of DidntSeeThatComing, this trope being the "that". Inverse of UnintentionalBackupPlan, where a character accidentally completes an imperfect plan that would have otherwise failed. Compare with OutGambitted, where someone's plan is successful but ineffective against a better-thought-out plan. Compare TooDumbToFool, where the character is too stupid even to be baffled by explanations. Also, compare EvilCannotComprehendGood, where the flaw is that the villain can't see someone being generous or brave or honest enough to foul up his plan.

Specialty of TheFool. See also DidntSeeThatComing, TheDogBitesBack, WhosLaughingNow

The trope is reputedly named for the [[OlderThanRadio Industrial Revolution]]-era practice of disgruntled workers throwing a spanner into a machine, either because of fears [[ScienceIsBad machines would put them]] [[LuddWasRight out of work]], or as a bargaining chip for better working conditions (and often because they were the only ones who knew how to repair the machines as well).

(Note for Americans reading this: "Spanner" is the Queen's English word for what you would call a "wrench", with the added benefit of it being slang for a stupid person. The equivalent American phrase specifically involves a ''monkey'' wrench, known in the UK as a gas grip -- "He really threw a monkey wrench into my plan.")

Disgruntled French workers did this by throwing ''sabots'' (wooden-soled clogs) into machinery - giving us the word '''sabotage'''.

'''Often an ending trope, spoilers may be ahead.'''
----
!!Examples
[[index]]
* [[SpannerInTheWorks.AnimeAndManga Anime and Manga]]
* [[SpannerInTheWorks.ComicBooks Comic Books]]
* [[SpannerInTheWorks.{{Literature}} Literate]]
* [[SpannerInTheWorks.LiveActionTV Live-Action TV]]
* [[SpannerInTheWorks.RealLife Real Life]]
* [[SpannerInTheWorks.VideoGames Video Games]]
* [[SpannerInTheWorks.WesternAnimation Western Animation]]
[[/index]]

[[foldercontrol]]

[[folder:Fanfiction]]
* ''VisualNovel/FateStayNight'''s fanfic [[http://www.fanfiction.net/s/6372400/1/Chaos_Theory# Chaos Theory]] opens up with this. It introduces the plots and manipulations of all the antagonists of FSN, and then the narrator calmly declares:
--> ''"But mostly? The assorted plans at play here would be going very, very wrong due to the actions of a no-name, no-count, utterly talentless Magus by the name of Shirou Emiya. He had no magic worth mentioning, no combat experience of note, and [[IndyPloy no plan for or knowledge of the War he was about to enter.]] He did, however, have one trait that had derailed a countless number of such grand, far-reaching schemes throughout history.''
--> [[SamaritanSyndrome ''You see, he really, really wanted to be a hero."'']]
* In ''[[FanFic/UltimateSleepwalker Ultimate Sleepwalker: The New Dreams]]'', the Green Goblin kidnapped and planned to publicly murder Gwen Stacy as a way to get revenge on her father, Captain George Stacy of the NYPD. While Franchise/{{Spider-Man}} intervened and tried to rescue Gwen, the Goblin had anticipated that and set things up so he'd be able to kill both Spider-Man and Gwen at the same time. Unfortunately, what he ''didn't'' take into account was Sleepwalker following Spider-Man to the [[ShoutOut top of the bridge]] a Cascnd distracting him long enough for Spider-Man to rescue Gwen and get her to safety. The Goblin proceeded to have a VillainousBreakdown.
* The ''FanFic/PonyPOVSeries'' has one that's notable for the exceptionally long time required for the spanner to actually get into the villain's works. [[spoiler:Back in the G3 Universe, which was facing TheEndOfTheWorldAsWeKnowIt (actually a ShootTheDog to avert a Class Z Apocalypse) at the time, Pinkie Pie's best friend Minty just bled to death after their fight with Luna, leaving behind her "spirit" (or at least a piece of herself). Strife, Discord's sister and Spirit of Natural Selection, is fighting the survivors of the doomed world (in order to give them at least the chance to fight for their survival, something she believes is the right of all living things) and sent Heartless-like spirits of "erased" ponies after them. One of these falls into the canyon where Pinkie and Minty's fight took place, wounded in battle. Pinkie, in a split second choice, fuses the piece of Minty with the shadow, which turns out to be that of the G1 Twilight. The result? ''[[TheHero Twilight Sparkle!]]'']]
** During the [[BadFuture Dark World Arc]], [[spoiler:Discord's little sister Rancor is this. She arrives to get close to Discord and ultimately steal back Destruction's power from him so it can be used for its intended purpose (Destruction's original job as an AnthropomorphicPersonification), mortally wounding him in the process. This ends up throwing a gigantic wrench in Nightmare Eclipse/Paradox's plans, allowing Discord to {{Out Gambit|ted}} her and alert Twilight to the [[GroundhogDayLoop true nature]] [[IronicHell of the Dark World]], forcing Paradox to expose herself to the heroes. The name Rancor chooses after succeeding (Disruption) couldn't be more appropriate. It's this trope especially because, while its implied she knew Paradox was there, she didn't care one way or the other what happened so long as her own mission was a success.]]
** Part 6 of Shining Armor's Arc has Sergeant Thunderchild be this [[BigBad General-Admiral Makarov]]'s attempt to kill Shining Armor. Makarov ''[[WhoAreYou didn't even know his name]]'', yet he shows up [[BigDamnHeroes just in time]] to break through Makarov's AntiMagic field and save Shining. This also buys time for more Shining's forces to show up in a GunshipRescue and drive Makarov's forces off.
** During the Wedding Arc, Prince Blueblood inadvertently foils Queen Chrysalis' plan just because he wanted to take a girl on a date. [[spoiler:He lead his date through the caves under Canterlot, and ended up finding the imprisoned Princess Cadance.]]
* In Evangelion fan-fic ''RE-TAKE'', SEELE finds all their plans foiled by something they could never have anticipated [[spoiler: Shinji be aided by [[ItMakesSenseInContext Ghost-Asuka and "God"]] which allows him to destroy the Mass Production Evas during the fan-fic's take the events of "End".]]
* In the Mario Fan-Fic ''FanFic/ClashOfTheElements'', [[spoiler: Fawful, Alpha and Mario are this to Cackletta's plans. And Bowser too, for freeing the Star Spirits from their imprisonment.]]
* Nanoha's presence in ''Fanfic/GameTheoryFanFic'' derails Precia's carefully laid plans. [[spoiler:But this turns out to be a subversion, because the events that disrupted Precia's original strategy actually made it possible for her to come up with a ''better'' plan that works flawlessly.]]
* The ''Manga/FairyTail'' AU fic ''[[http://www.fanfiction.net/s/4711916/1/Lost-Magic Lost Magic]]'' is an interesting example. While the deliberate wrench in Jellal's plans is Simon, the one whose mistake actually set his plot derailing was [[{{Irony}} Jellal, himself]]. [[ItMakesSenseInContext By accidentally getting himself pregnant with Erza's child.]]
* ''FanFic/JewelOfDarkness'': The only reason Midnight's plan to [[spoiler:torture Robin to insanity]] fails is because [[spoiler:[[MookLieutenant Ai]] [[TheStarscream betrays her]] on orders from [[BiggerBad Trigon]]]], something she ''couldn't'' have possibly anticipated.
* ''FanFic/QueenOfAllOni'': Jade's [[DangerouslyGenreSavvy otherwise flawless]] [[OperationBlank Operation: Steel Lightning]] only fails because of the presence of Agent Wisker, who she didn't know and couldn't plan for. He doesn't stop her, but slows her down long enough for Uncle to catch up with her and beat her.
* In ''Fanfic/{{Kage}}'', Yua predicts [[WesternAnimation/JackieChanAdventures Jade's]] presence in [[{{WesternAnimation/WITCH}} Meridian]] will cause Nerissa's plans to go OffTheRails, and any attempts by the elderly sorceress to force Jade to fit in her plans will only cause the schemes to unravel further. Jade is also this to the second season timeline in general, with the changes already starting to add up.
* ''FanFic/AnAlternateKeitaroUrashima'' repeatedly derails his grandmother's attempts to manipulate him simply by letting others know how [[ManipulativeBitch manipulative]] she is. As a result, when she shows up and starts spinning her webs, she winds up proving him right.
** Mokoto also runs afoul of this when she threatens Keitaro one time too many. When she draws her katana, she's unaware that [[spoiler:some police officers are passing behind her and witness it]].
* ''Fanfic/DeathNoteEquestria'': Mer ends up [[TheStarscream going off Twilight's script]] in order to ruin her in revenge for [[spoiler: Rarity]]'s death as a part of one of Twilight's earlier gambits. [[spoiler: Subverted, however, as Twilight had actually anticipated this and factored it into her plans, resulting in Twilight's triumph and Mer's death.]]
* ''Fanfic/NedStarkLives'' reveals that Jaqen H'ghar had been hired by [[spoiler:the Great Other]] to kill [[spoiler:Jon]]. Arya's presence in the Night's Watch caravan completely derailed that plan, though.
[[/folder]]

[[folder:Films -- Animated]]
* Oh, the joys of ''WesternAnimation/ChickenRun'' - this is one of many visual gags, and surprisingly one that is relevant to the plot.
* The title character of ''Disney/WreckItRalph''. His desire to gain the fame and respect his rival, Fix-It Felix, Jr., had, even unwittingly, lead to [[spoiler:''Sugar Rush'''s King Candy being exposed as the thought-dead Turbo and the restoration of glitch character Vanellope Von Schweetz.]]
* ''WesternAnimation/MonstersInc'': According to [[spoiler:Roz]], Sulley and Mike were this to [[spoiler:Waternoose's plan]]. She gives them credit for exposing the scandal when [[ReverseMole she reveals her own true colors]].
-->'''[[spoiler:Roz]]''': Two and a half years of undercover work were almost wasted when you intercepted that child, Mr. Sullivan. Of course, without your help, I never would have known that this went all the way up to [[spoiler:Waternoose]].
* ''Disney/{{Frozen}}'':
** [[spoiler: Olaf]] was this. [[spoiler: With Kristoff having left the castle when Anna was about to die, Hans' plan may have succeeded and given him the throne.]] But there was no way to account for [[spoiler: Olaf, who saves Anna.]]
** Elsa was also this. [[spoiler: Her denial of Anna's marriage to Hans and her departure from Arendelle wound up saving Anna as it delayed his plans and gave Anna a lesson in trusting people so quickly while at the same time showing her ThePowerOfLove.]]
[[/folder]]

[[folder:Films -- Live-Action]]
* The ending of ''Film/LayerCake'' has the protagonist outclassed not by dumb luck, but by [[spoiler:being shot.]] Because while he was really successful in tricking clever criminals in his BatmanGambit, he [[spoiler:ends up shot (and possibly killed, it's a little vague) by a guy whose girlfriend he stole and whom he considered of little importance.]]
* ''Film/CarlitosWay'' ends in a similar fashion. After outsmarting all his enemies by the skin of his teeth [[spoiler:Carlito ends up getting killed by some random lowlife he mistreated earlier in the film.]]
* Before both above films, you have ''Film/NewJackCity'', where drug kingpin, Nino Brown, is able to fast talk his way out of serious prison time, only [[spoiler: to get killed by an old war veteran]] he didn't take seriously during the film.
* ''Franchise/StarWars'' has a few examples:
** The Ewoks in ''Film/ReturnOfTheJedi'' are the one tiny overlooked factor that brings the Emperor's entire grand scheme crashing down.
** Luke just happens to wound Vader in the same way Vader wounded him, thus making Luke realize what he had [[WhatHaveIBecome almost become]]. Of course, [[http://www.irregularwebcomic.net/462.html the Emperor really wasn't helping his own cause, either.]]
** The Expanded Universe has the entire Imperial Fleet artificially boosted by the Emperor's force powers. The Emperor's death ended up causing the imperial officers to lose control of the situation, preventing them from shooting down the Millennium Falcon before it could destroy the Death Star 2.
** There's also [[TheScrappy Jar Jar Binks]], whose clumsiness is more than a match for several ''tanks''.
** There are [[ContinuitySnarl about a dozen ways]] the Rebels lucked into the plans for the Death Star in the [[Franchise/StarWarsExpandedUniverse expanded universe]]. By now you'd think they had enough plans to spare.
** Anakin Skywalker's destroying the Trade Federation's droid control station in the first prequel was a massive stroke of luck. To the extent that not even ''he'' realized what was happening. He just hid in an unmanned Naboo fighter and stuff happened.
* The scheming husband in ''Film/DialMForMurder'' is undone because he underestimates the intelligence of Swann/Lesgate, the thug he hired to kill his wife. Swann puts the key right back after using it, rather than keeping it, as his employer expected.
* In the recent adaptation of ''Franchise/ThePinkPanther'', it seems like Inspector Clouseau, a seemingly InspectorOblivious is one of these until the very end, where he reveals that he was a Chessmaster after all. According to Creator/PeterSellers, the original Clouseau qualified as well, but he knew he was a buffoon deep down. ''Strikes Again'' had killers from all over the world come after him. [[spoiler:He bends over to tie his shoes at the exact right moment...]] Likewise in the film's {{Denouement}}, [[spoiler: Clouseau is unwittingly catapulted onto Dreyfus' DeathRay, destroying it and killing Dreyfus in the process.]]
* ''Film/SweeneyToddTheDemonBarberOfFleetStreet'': Sweeney Todd would have killed Judge Turpin and ended the movie right there and then in the middle had Anthony, who had recently talked to Sweeney about his plan to elope with Johanna in order to get her away from Turpin, not busted into his shop ''with the judge right there in the room'' in order to inform Sweeney that he has found Johanna and that she has agreed to the plan. Needless to say, this ends up blowing both the aforementioned plan and Sweeney's attempt to kill Turpin straight to hell.
* All throughout ''Franchise/PiratesOfTheCaribbean: Curse of the Black Pearl'', Jack repeatedly plots for the most favorable outcome (for himself), but stubborn fool Will Turner and arrogant {{jerkass}} Captain Barbossa assume they know best how to get things done, and nearly screw themselves out of their goals frequently. If Barbossa had wanted to cut Elizabeth's throat instead of her hand, Will would've been too late to save her on his own, and if Will had died like he should've when Barbossa ordered the Interceptor scuttled with Will trapped below, Barbossa would never have gotten Will's blood to pay Bill Turner's debt. Near the end of the film before the climactic battle, Jack has everybody where he wants them, but because Barbossa and Norrington don't trust him at all, his plans almost fall apart.
** That's what Jack WANTS you to think.
* In the 1932 sci-fi mystery film ''Film/DoctorX'' the MadScientist SerialKiller manages to not only [[spoiler:trick the other characters into believing he is innocent]] but also [[spoiler:manipulates them into physically restraining themselves so he can slaughter them at his leisure]]. Unfortunately he forgot about the PluckyComicRelief IntrepidReporter, [[spoiler:who manages to dispatch him in a terrified and bumbling fashion at the last minute]].
* In TheCaper film ''Film/TheKilling'', a band of criminals pull off an elaborate robbery of a racetrack. Even though the [[spoiler:most of the criminals kill each other off fighting amongst themselves]], the AntiHero and his {{Love Interest|s}} manage to [[spoiler:escape to the airport and prepare to board a plane out of the country with all the loot]]. However, all their plans are foiled when [[spoiler:a dog runs out in front of the luggage train, causing it to crash and spill the loot all over the runway for all to see]].
* In ''Film/TheManWhoKnewTooLittle'' the main character foils a terrorist plot without even knowing there was one.
* By refusing to sacrifice each other, the passengers on the two boats in ''Film/TheDarkKnight'' end up being this for The Joker, in that his social experiment in proving that anyone could be corrupted ends in failure.
** In ''Film/BatmanBegins'', Batman himself is the Spanner towards [[spoiler:Ra's al Ghul]] and the Scarecrow's plan to destroy Gotham.
** And in ''Film/TheDarkKnightRises'', [[spoiler:Catwoman]] serves as one when [[spoiler:she saves Batman from Bane]] in the climax.
* In ''Film/CastADeadlySpell'', [[spoiler:the Evil Necromancer's plan to summon Cthulhu is thwarted when it turns out his daughter was no longer a virgin due to the idiot cute cop nobody had been paying much attention to.]]
* The terrorists from ''Film/VantagePoint'' might have gotten away with it, had it not been for a ''little girl''.
* In ''Film/TheATeam'', [[spoiler: Face's plan]] would have gone off smoothly if not for [[spoiler: Pike having a [[http://en.wikipedia.org/wiki/Shoulder-launched_Multipurpose_Assault_Weapon SMAW]].]]
-->'''Pike''': Here's what I think of your best laid plans!
--> * Pike fires the SMAW into the ship's hull*
* CowboyCop [[Franchise/DieHard John McClane's]] ''real'' job. When terrorists are confidently moving chess pieces behind the scenes, he knows that all he has to do is look for something sensitive and start whaling on it.
* ''Film/TheAdjustmentBureau'' tries to contain this kind of incidents. But they are not above random chance and unexpected behavior.
* BadassBystander Gina in ''Film/{{Unknown 2011}}''. Despite just being his cab driver, she saves Dr. Harris' life at the beginning of the movie and twice afterwards, [[spoiler:killing {{Mooks}} and the BigBad in the process,]] which also allows Harris to stop the plan of the BigBad.
* In ''Film/AFewGoodMen'', it becomes apparent that the Department of the Navy very much wants the case of ''United States v. Dawson & Downey'' to be quietly resolved by a PleaBargain so as to prevent incident from causing too much embarrassment to the Marine Corps. This plan is undone by the dual spanners of Galloway and Dawson; Galloway, not because she is dumb, but be because she is clever enough to sense something in not right and thus goads Kaffee in doing his due diligence for once instead of rushing to a PleaBargain, Dawson, for being too hardcore of a jarhead to willingly accept a dishonorable discharge because it would make thing easier for him, and telling Kaffee to take his plea bargain and shove it.
* In ''Film/TheAtomicBrain'', as shown on the TV series ''Series/MysteryScienceTheater3000'', in spades. The main plot for the villain Miss Marsh was for her to have her brain swapped with the prettiest girl of three chosen. That gets ruined when the homeliest of the three, who had her brain swapped with the cat's, [[EyeScream gouges her eye out]]. Miss Marsh's companion tries to double-cross her, killing her and letting the remaining girl take her money, but Marsh kills him. The scientist, Dr. Otto Frank, pulls one by placing Miss Marsh's brain with the cat's, revealing that he wanted to keep her locked away in the cat so he could use her money to continue his research on reviving the dead. Miss March responds by locking him in the revival chamber and setting the dial to "Frag the entire house".
* ''Film/TheAvengers''.
** Had Thor not been there to keep the Hulk at bay the Helicarrier would have crashed and Loki's plan would have more than likely been successful.
** The arc reactor in Tony Stark's chest. [[spoiler: It prevents Loki from mind-controlling him and turning him against his allies, which would have derailed everything just as much as the Hulk's potential rampage.]]
* Kirk in ''Film/StarTrekIntoDarkness''. [[spoiler:By threatening Harrison and offering him a chance to surrender, rather than killing him from afar as ordered, he single-handedly and accidentally derails all of Admiral Marcus' plans]]. And Spock, who drove him toward that decision.
* ''Film/ForrestGump'' calls to complain that he can't sleep because of people playing with flashlights in the next building over and so [[HistoricalInJoke blows the lid on Watergate]].
* In ''Film/TheLadyVanishes'' an oblivious Iris manages to completely destroy a Nazi conspiracy just because she won't give up insisting that the eponymous lady exists.
* ''Film/{{SWAT}}'': [[BigBad Alex Montel]] kills his uncle Martin Gascoigne for sticking his hand in TheSyndicate's till, then takes Gascoigne's car to the airport to catch his flight home. On the way, he's pulled over by a motorcycle policeman because he has a tail light out. The officer then discovers there's an arrest warrant linked to the license plate and detains Montel "until we can verify who you are." {{Lampshaded}} by an FBI agent after Montel's identity is discovered:
--> "We've been lookin' for this guy a long time. Busted tail light brings him down? That's amazing."
** This type of thing is very much TruthInTelevision, many real criminals are caught because of insignificant things that shouldn't have happened. One notable example is Timothy [=McVeigh=], who was also caught when he was pulled over by a state trooper.
* In ''[[Film/{{Oceans 11}} Ocean's 11]]'', all it takes is [[spoiler:Anthony Burgdorf's widow deciding to have his funeral in Las Vegas]] for Operation [[spoiler:Pine Box]] to go to hell.
* This concept drives the entire plot for ''Film/DumbAndDumber'. Lloyd sees Mary "forget" her briefcase while going through the airport, and, desperate to win her affection, races through the airport to snag the briefcase and return it to her:[[spoiler: the briefcase is the drop for a ransom, containing millions, left there to be picked up by a few hired thugs.]] The entire plot also runs because the crooks think that Harry and Lloyd are merely ObfuscatingStupidity, never understanding that no, they are actually that dumb, but happen to thwart the criminals at every turn.
* In ''Film/KingsmanTheSecretService'', Valentine's plan would have gone off without a hitch if Harry hadn't pulled Eggsy to his place to yell at him, allowing Eggsy to watch the video transmission of the church events. This directly led to Eggsy realizing that [[spoiler:Arthur was compromised and allowed him, Merlin and Roxy to take Valentine down before the evil plan was completed]].
* In ''Film/DayOfTheWolves'', #1's plan for TakingOverTheTown was masterfully planned and executed. The one thing he could not have forseen was that Chief of Police Pete Anderson would have been fired the day before the plan was executed, and therefore was at home instead of at the police station with the other officers.
[[/folder]]

[[folder:Music]]
* Invoked, if only as pastiche (which Morrissey ''adores'', as we know) in Music/TheSmiths' title track "The Queen is Dead":
-->So I broke into the Palace \\
With a sponge and a rusty spanner
** ...referencing a peculiar event--long forgotten by most, perhaps--though the unlikelihood of [[http://news.bbc.co.uk/onthisday/hi/dates/stories/july/9/newsid_2498000/2498731.stm Michael Fagin's misadventure]] conveys this trope's inherent flavor of the unexpected. In the BBC's retrospective, we learn "[t]he Queen was only able to raise the alarm when he asked for a cigarette." In more security-conscious days, who'd imagine such a Royal [[FishOutOfWater contretemps]] could occur at all?
[[/folder]]

[[folder:Tabletop Games]]
* In just about any [[TabletopGame/DungeonsAndDragons D&D module]], the adventurers are the Spanner. And any good GM has to be able to handle a Spanner, as the [=PCs=] can be expected to do [[OffTheRails the one thing the GM hasn't anticipated]].
** A mediocre GM can do this to players. When the players have a good plan which bypasses the intended challenge handily or solves a challenge with minimal fuss, a good GM may let the players have their moment in the sun and save those encounter notes to recycle them with new window dressing. A mediocre GM will have the players' plans fail for increasingly implausible reasons. A poor one will have a deer in headlights look as soon as the players are OffTheRails.
** Example: Give the [=PCs=] the Eye of Vecna, you get some fun people fighting over it. However, one of the [=PCs=] sacrificing the Eye of Vecna to THE GOD OF JUSTICE? Not so expected.
* In ''TabletopGame/UnknownArmies'', you can become an Avatar of [[CharactersAsDevice an archetype]] by mimicking that archetype's classical behavior. One of those is TheFool, who can pull this off easily and walk away unscathed.
* In ''TabletopGame/{{Chrononauts}}'', new players are the spanner. Plans in the game range from GambitRoulette to "I win next turn as long as no one makes a minor change in 1914". New players will often meddle with history (even ''starting WorldWarIII''), steal random historical artifacts, or kill the makers of said artifacts, to "see what happens".
* In ''TabletopGame/{{Exalted}}'', beings that exist outside of fate are the ultimate Spanners from the perspective of the Sidereals. Since they cannot be detected, manipulated, or predicted by fate and fate-based powers, one of these beings can derail centuries of careful planning before the Sidereals realize that anything's amiss.
* In ''TabletopGame/VampireTheRequiem'', the Circle of the Crone has the position of TheFool, whose sole purpose is acting as this. When the Circle needs something stopped they send in TheFool and watch stuff blow up. Basically it's like "so, you're a rather spirited walking corpse, eh? Say, could you go check out what that Invictus bastard is doing downtown? Just do whatever feels natural, I'm sure it'll be a blast." Fools who survive long enough to gain some measure of respectability might make it to the rank of [[TheTrickster Trickster]], for whom the purpose is basically the same except the Trickster actually has some idea of what he is doing.
* A common meme in ''TabletopGame/{{Warhammer}}'' and ''TabletopGame/{{Warhammer 40000}}'' is to label the defeat of [[TheChessmaster Tzeentchian and Eldar forces]] as "Not As Planned"; as the smug bastards claim any victory is "[[AllAccordingToPlan Just As Planned]]".
* In ''TabletopGame/Champions 5th edition universe, The centuries long, multi-dimensional, wheels within wheels master plan of DEMON's secret master involves in it's final stages a literal Spanner in the Works. The precise timing that underlies the multiverse needs to be off just slightly for the rest of his plan to work and as such he has positioned a minion in the the metaphysical boiler room of creation with a $10 hardware store spanner. Now he just needs the stars to align....
[[/folder]]

[[folder:Theatre]]
* Theatre/CyranoDeBergerac: Played hilariously straight: This play (a farce) has a lot of GambitPileup orchestrated by [[TheProtagonist Cyrano]], [[LoveInterests Roxane]] and [[TheAntagonist De Guiche]], but no one of them is capable of being an UnwittingPawn for long.
** Cyrano: Lampshaded by himself at Act II Scene VI: Unaware of it, he destroys De Guiche plan to set an arranged marriage with Roxane and De Valvert when he manipulates De Valvert to a duel.
--> '''Cyrano:''' ''(Bowing to Roxane):''
--> Then I fought, happy chance! sweet lady, not
--> For my ill favoróbut your favors fair!
** De Guiche: When you apply FridgeLogic, you see that De Guiche was the UnwittingInstigatorOfDoom in his own plan to [[ArrangedMarriage bully Roxane into a marriage]] with [[TheBeard De Valvert]] at Act I Scene IV: When De Guiche makes a DareToBeBadass to De Valvert, itís only a small act, but itís crucial because it sets a DisasterDominoes scenario that ends with De Valvert being touched by Cyrano and so unable to marry Roxane. He also destroys his own plan to BuyThemOff Cyrano when he mentions that his uncle Richelieu could correct a line or two from Cyranoís work.
[[/folder]]

[[folder:Visual Novels]]
* ''Franchise/AceAttorney'':
** [[spoiler:Kristoph Gavin]]'s ultimate scheme in ''VisualNovel/ApolloJusticeAceAttorney'' was meant to be the murder of [[spoiler:Vera Misham]] via a poisoned postage stamp depicting the magician act Troupe Gramarye. However, the girl is such a huge fan of the Troupe that she saves the stamp for seven years; [[spoiler:her father]] eventually uses the stamp instead and dies. The flaws in [[spoiler:Gavin]]'s plans run deeper than this, but this is his only apparent mistake; everything else is because of [[spoiler:Phoenix Wright]]'s meddling.
** Larry Butz also counts, owing to his tendency to do unreasonable things that end with him [[ShaggySearchTechnique stumbling onto vital evidence]]. In the first game, he [[spoiler:was coincidentally returning a boat he had been using at precisely the right time to overhear a gunshot]], in the third he [[spoiler:shirked his work as a security guard when the villain's plan relied on him being at his post so that he would hear the noise of a panic button, rush into the room and arrest the wrong person]] and then in a later case his choice to [[spoiler:wander around at night in the cold]] leads to him [[HeKnowsTooMuch witnessing a number of things he wasn't meant to]].
** In the fourth case of ''Justice For All'', the lead that helps Gumshoe and company track down Shelly de Killer is, of all things living and not living, [[spoiler:Matt Engarde's ''cat'', who meows at the end of a transmission from de Killer]].
** In the third case of ''Justice For All'', [[spoiler:Acro's plan to murder Regina was to call her to a specific point where he would drop a heavy weight on her head. Problem is, the note he secretly planted on Regina began with "To the murderer...". Due to Regina being very naive, she didn't think the note was for her, and posted it on the circus's bulletin board, where her father saw it and responded to it in Regina's place.]] Then you realize that [[spoiler:Acro wanted to kill her because her naivete led to his brother being put into a coma, [[WhatAnIdiot and he should have known that she would never realize the note was meant for her]]...]]
** In the final case of ''VisualNovel/AceAttorneyInvestigations'', the shenanigans of [[spoiler: Larry Butz and Wendy Oldbag, of all people]] end up helping Miles Edgeworth put away the seemingly untouchable BigBad. [[spoiler:Larry, by accidentally breaking the Samurai Spear, forces the staff to have the Steel Samurai use a different move instead, thus enabling Edgeworth to realize that Alba was not at the Steel Samurai show while he was killing Manny Coachen. Wendy Oldbag takes the box of "Rising Sun Dogs," which turns out to have a drop of Alba's blood on it, and combined with Alba's wound, proves that he was injured while killing Coachen]].
** Larry gets to do this again in the manga. Simply by being arrested on suspicion of killing Bright Bonds (based on calling him and demanding that he get out of his ex-girlfriend's life), he derails the killer's plan to [[spoiler:use him as an alibi, because ''she'' gets called in to prove ''his'' alibi, and through contradictions in her testimony, gets implicated as the murderer]].
* In ''VisualNovel/VirtuesLastReward'', [[spoiler:Dio]] aspires to be one for the AB Game. [[spoiler:Too bad for him that not only is his presence expected, it is in fact required.]]
* The PlayerCharacter can potentially become this in VisualNovel/TrueLoveJunaiMonogatari, if following [[spoiler: Ryouko Shimazaki]]'s route. [[spoiler: Ryouko is actually an IdolSinger (under the identity of Sonoko Takahashi) and has apparently retired, much to the sadness of her fans '''and''' the profit of her sponsors. Her manager and [[PromotionToParent brother/parent figure]], Tadaaki, actually had her ''fake'' her retirement to pique the interest of the fandom, then make the greatest come back ever -- and since Ryouko is both his younger sister and his ward, she cannot stop him no matter how badly she [[IJustWantToBeNormal wants to lead a life od her own]]. But after she befriends the MC, he inspires her to try speaking up and [[BeYourself being her own self]], leading her to rebel against the [[StageMom stage brother]] who controls her life and actions.]]
** Also, if the PC pursues [[spoiler: either Mayumi Kamijou or Yumi Matsumiya (who can't be romanced if you don't finish Mayumi's path first)]], he will also ruin [[spoiler: Mikazaki's plan to blackmail Mayumi into sex]] ''and'' will [[spoiler: give Yumi enough proof to get Mikazaki himself humiliated and kicked out of the school.]]
[[/folder]]

[[folder:Web Animation]]
* In the ''WebAnimation/HomestarRunner'' holiday toon [[http://www.homestarrunner.com/xmas08.html "A Death-Defying Decemberween"]], Homestar announces to one and all that he's going to sled down the Steep Deep - a ''vertical cliff face'' - and Strong Bad catches The Cheat surreptitiously helping Homestar bury a mattress at the foot of the alleged slope. Of course, Strong Bad being Strong Bad, he moves the mattress expecting Homestar to maim himself on impact...but the next day, when Homestar sleds down the Steep Deep, he makes a perfect landing. As it turned out, the mattress was full of "hammers, broken glass and candy canes sucked down 'til they're all pointy"; the whole thing was a ridiculously elaborate (and painful) scheme for Homestar to get out of having to spend Christmas with his girlfriend [[GranolaGirl Marzipan's]] parents, one that Strong Bad successfully sabotaged (even if the end result wasn't ''quite'' what he had been expecting).
* In ''WebVideo/YuYuHakushoAbridged'':
--> '''Kurama''': ''"...so I believe Hiei's superior speed would be the best choice for this fight."''\\
'''Hiei''': ''"Well Kurama, your plan sounds good except for one fatal flaw."''\\
'''Kurama''': ''"What? What are you talking about? My plan is foolproof!"''\\
'''Kuwabara''' ''(screen-shift)'': "''Here kitty kitty!''"\\
'''Kurama''': ''"I stand corrected.''"
[[/folder]]

[[folder:Web Comics]]
* In the ''Webcomic/SluggyFreelance'' story arc "[[http://pics.sluggy.com/daily.php?date=010611 GOFOTRON Champion of the Universe]]," Zorgon Gola has a pretty nice [[BatmanGambit Gambit]] set up where he ''pretends'' to be an OmnicidalManiac, so that the heroes will sacrifice themselves trying to prevent a chain reaction that would destroy the universe, leaving him free to [[GalacticConqueror take over the Punyverse]] after their deaths. What he didn't count on was Torg, Riff, and Bun-Bun accidentally teleporting themselves into the Punyverse. They end up hijacking a vital piece of the heroes' CombiningMecha (the crotch). Without this, the heroes have no way of pulling off their HeroicSacrifice, and Zorgon Gola, along with the rest of the Punyverse, is blown up. [[MikeNelsonDestroyerOfWorlds Oops]].
* Obi-Wan and Qui-Gon end up doing this to [[spoiler:Darth Maul]] in ''Webcomic/DarthsAndDroids''. In a clever little inversion, this whole scenario is actually made up on the spot by the DM, ''after'' the events took place in which the players apparently screwed up everything by going OffTheRails. The author suggests this technique as a way of [[{{Railroading}} getting back at players who mess with your established scenario too much.]]
* Quentyn Quinn in ''Webcomic/TalesOfTheQuestor'' is a subversion. Instead of stupidity, it is a sense of honor and desire to help that make him accept quests which almost always indirectly monkey-wrench SOMEONE'S plans, generally without even knowing it. Examples:
** [[ConvictionByCounterfactualClue A simple lack of knowledge]] led him to believe (and say) that human coins were forged. A politician's OhCrap moment led a guard to realize [[RightForTheWrongReasons they were indeed fakes]]--and who was behind it.
** His very decision to become a Questor--paired with the discovery of an old contract--puts his home village in peril. The contract stated that the previous Questor was to retrieve some artifacts in exchange for land on which to build a village. The problem: the old Questor failed to do so, and now that there's a new Questor, a political faction intends to use that contract to get Freeman Downs repossessed and thus out of the picture. Quentyn's decision? Retrieve those artifacts, knowing that if he dies in the attempt, the law ensures that the contract ends with him. He knows nothing about the true scheme at work, and the opposing faction has no idea what to do now. The legal counsel sent to deliver the bad news summed this trope up rather perfectly:
---> ''"[[http://www.rhjunior.com/totq/00370.html Your Questor made a move they completely failed to prepare for. Unsurprising; I've found schemers and plotters are rarely able to cope with simple things like honor and courage.]]"''
** His desire to help a human village ended with him in a position to UTTERLY screw over a fae--[[GoodIsNotNice which he does]] so very EPICALLY.
** And then there's Squidge, who is only too happy to prove that one can ''deliberately'' be this when he ruins Rahan's prank.
* Fighter of ''Webcomic/EightBitTheater'' is the living embodiment of this trope, as he's too [[TooDumbToLive stupid]] to know whether he's supposed to fall for a crazy plan or not. He bends the TheoryOfNarrativeCausality by his very existence.
* Roy Greenhilt of ''Webcomic/TheOrderOfTheStick'' qualifies for this in one early instance, despite being a very intelligent person, simply because he does something so very unexpected. Xykon honestly doesn't expect the heroes to stop him (and rightly so, as he has an army of monsters, 10 or more levels on the strongest PC, and a monster strong enough to send Paladins flying by LIGHTLY TAPPING THEM). He has three characters immobilized, two more being stalled by monsters, and he had JUST shattered the leader's ancestral sword. Confident that the battle is as good as over, he starts to call out the aforementioned monster to finish the heroes off. And then Roy goes and tosses his bony ass into a body-destroying gate that holds an EldritchAbomination at bay. The BigBad is out of commission.
** [[IdiotHero Elan]] is one of these for both the good and bad guys. Daigo at one point wonders if he's more useful the less he knows what's going on, and Durkon [[http://www.giantitp.com/comics/oots0558.html suggests]] that "He has Ignorance as a class power source." In [[http://www.giantitp.com/comics/oots0691.html 691]], Roy lets him wander around the desert in the hopes that he'll stumble over something. [[http://www.giantitp.com/comics/oots0727.html WHICH HE DOES!]]
* ''Webcomic/AntiheroForHire'''s [[http://www.antiheroforhire.com/d/20080317.html Wizard]] lays it out cold for would-be [[TheChessmaster Chessmaster]] Hector:
-->You always overthink things. The reason your plans keep failing is not because your enemies are geniuses. It's because they are idiots. A plan is only truly foolproof if you consider the fool.
* In ''Webcomic/DeadOfSummer'', the BigBad's [[CrazyPrepared backup plan]] to blow everyone up with a TimeBomb was thwarted because [[spoiler: Tito and Otis saved [[Music/TheProtomen Panther]], who proceeded to disarm the bomb and save everyone.]]
* The majority of the plot of ''Webcomic/{{Demonology101}}'' consists of Raven and her friends following this trope.
* One of the characters in the ''Webcomic/{{Blip}}'' is this to [[spoiler: God's master plan.]]
* The main cast of ''Webcomic/{{Drowtales}}'' are {{Manipulative Bastard}}s and [[TheChessmaster Chessmasters]] whose plans often wind up [[GambitPileup crashing into each other]], but so far the biggest example of this trope is [[spoiler:Ragini, a child slave who survived the massacre at the Val'Sharess tower and was able to keep said Queen alive for a year, and then later become host to her aura and escape]]. If it weren't for her things in the story would be much, much different, and the full extent of her spanning potential is just beginning.
* A smaller version in ''Webcomic/GirlGenius'' --British spy/Gil's man Wooster just caused [[spoiler: Dolokov's plan to corrupt/distract the Jaegergenerals while Wulfenbach forces destroy Castle Heterodyne]] to go thoroughly off the rails.
* In Season 9 of ''Webcomic/SurvivorFanCharacters'', Prescilla/Bonnie has been controlling the entire game and has managed to take the two weakest players to the finals with her while tricking everybody into believing that she's just a [[BitchInSheepsClothing sweet, innocent girl who couldn't POSSIBLY be an evil mastermind]] and [[EvilGloating gloats]] about how she has a 100% chance of winning the day just before the final Tribal Council. Then Cherman, the little robot who has been a ButtMonkey for most of the game, reveals that he has a recorder he used to record Bonnie's EvilGloating about how her only regret is that she didn't do more to hurt others. Your reign was nice while it lasted, Bonnie.
[[/folder]]

[[folder:Web Original]]
* When LetsPlay/TippingForties LP'd ''VideoGame/TalesOfSymphonia'', they managed to go about 90 videos without using Presea, who they perceived as TheScrappy. The point was they hated the flatness of the character and refused to involve themselves with how stupid that part of the game was. Of course, they forgot the game was stupid (for that one instance, at least) and a scripted event forced them to use her. It nearly brought them to tears. [[LaserGuidedKarma And it was]] ''[[CrowningMomentOfFunny Hilarious]]''.
* In the ''Literature/WhateleyUniverse'', this is Jade's purpose in life. She's screwed over at least four {{plan}}s, simply by being there. See "It's Good to be the don", "Christmas Elves", "Christmas Crisis", and Ayla 7-6.
* It's extremely rare for this to not happen at least once per game in ''Roleplay/ComicFuryWerewolf''. It also happens intentionally a surprising amount, considering.
* Boomer, a MadBomber from the Wiki/SCPFoundation storyline "Game Day", tends to carelessly leave dangerous explosives in random places around his hideout, to the point that it's not really possible to plan a safe approach to it.
-->Boomer was the type to leave loads of bombs, traps and other assorted goodies laying around in a [[GeniusDitz nightmare combination of cunning and blind, absentminded stupidity]]. You could plan around a smart enemy, a dumb one was prone to blowing your intelligent, well-planned ass off at random.
* The "Heist" episodes of Creator/AchievementHunter's ''[[LetsPlay/AchievementHunterGrandTheftAutoSeries Let's Play Grand Theft Auto V]]'' always have one that ruin their well thought-out robbery plans [[spoiler:towards (usually) a convenience store]].
** The first episode "(Geoff's) Heist" gets derailed when their explosions causes their wanted level to hit 3-star, bringing in a helicopter.
** "Gavin's Heist" goes bad when the explosives on the tanker truck they were using despawned due to distance.
** "Ryan's Heist" got derailed due to just how much trouble the gang was having trying to get the Cargobob to the armored truck.
** "Michael's Heist" hits a minor snag when he realizes that he can't rob banks yet ([[DevelopmentHell Rockstar hadn't added that in just yet]]), but recovers spectacularly.
** "Jack's Heist" gets hit because of the escape jet they were using - they couldn't escape cleanly in traffic and later [[spoiler:roasts Michael, who had the money.]]
** "Ray's Heist" goes belly up because of a locked armored car door.
** "The Grand Heist" stumbles at the finish line because the Titan stalled.
* In ''WebOriginal/TenLittleRoosters'', [[spoiler:Chris]] just can't ''die'', preventing Burnie from getting the killer ''four times in a row'' because he keeps acting like [[Film/LordOfTheRings Boromir]].
[[/folder]]
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