Someone unintentionally plays a small and/or unlikely but crucial role in some horrible development (usually this action serves as the catalyst).
An Unwitting Instigator of Doom can be basically complicit with the villain, but in that case, they're generally seeing only a small portion of the picture. If they're being specifically manipulated but do not realize, they're an Unwitting Pawn. Other times, they're simply blundering in like a wrench in some particularly highly valued machine, so it can be caused by The Load or The Millstone. They may also end up as the Idiot Houdini. In the worst cases, more in the know characters will chew them out for bumbling in and screwing things up, trusting them little better than they would a traitor.
Compare Nice Job Breaking It, Hero for when the heroes cause doom, and Mike Nelson, Destroyer of Worlds for a different type of unwilling doom bringer. Also compare Chekhov's Gunman, in which a seemingly insignificant character becomes more important later on. See also Interrupted Cooldown Hug, Endangering News Broadcast, Tragic Mistake, and Small Role, Big Impact.
No Real Life Examples, Please! Aside from being prone to misuse, it is likely to invite Flame Wars.
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- Western Animation
- Alexander Afanasyev's "The Soldier And Death": If the third beggar had not repaid the soldier's kindness by giving him a magic pack of cards and a magic bag, the man most likely would have not tried to kick a band of demons out of the tsar's palace, and he would not have tried to imprison Death itself to save his life, hence he would have not been barred from the afterlife.
- Mrs O'Leary's cow, who kicked over a lantern which ignited straw in her stall which ignited the wall which led to the Great Chicago Fire of 1871. The reporter who first publicized this origin later admitted to making it up.
- In Alan Walker's extended universe, it's revealed that 28300 financed her expeditions by collaborating with Red Nexus corporation. Doing so gave Red Nexus unlimited access to the Walkers ancient advanced technology, which they used to try to conquer the world.
- Nena's song "99 Luftballons" (and its English version "99 Red Balloons") tells a story of a young couple who release 99 balloons to celebrate their love. The balloons are picked up by military radar and trigger a war that levels the city.
- In Dungeons & Dragons: Fifth Edition adventure Out of the Abyss, the drow Gromph Baenre serves as this for the party. Granted, Vizeran DeVir mentions that Gromph trying to summon a demon lord of the Nine Hells was an incredibly stupid move, all on its own. But it's thanks to interference from the Chaotic Evil Lolth that Gromph summoned all of the demon lords instead, causing them to wreak havoc across the Underdark, including to the City of Spiders that Gromph's sister rules. It also turns the party's quest from escaping the Underdark into stopping the demon lords by any means necessary. And even then, countless people end up dead thanks to Gromph's decision.
- Magic: The Gathering: Lamar, a barbarian sentry from Judgment who sees Jeska knocking Kamahl's friend Balthor unconscious, and, believing she's killed him, rushes to tell Kamahl, who attacks Jeska in a fit of rage, mortally wounding her. This leads to the Cabal finding Jeska and saving her life by transforming her into Phage the Untouchable, kicking off the apocalyptic events of the entire Onslaught Cycle. Which, as it turns out, led to the fabric of existence being marred so much that temporal rifts began opening across all of the Multiverse (at various points in spacetime, no less); these rifts were revealed to be the causes of some key events that led to the Kamigawa and Mirrodin blocks, and finally culminated in permanently warping the very nature of all Planeswalkers Sparks both currently held and from that point forward. Because one private didn't check the body, the Multiverse was forever changed.
- Warhammer Fantasy:
- In the backstory, the ancient Dwarf Empire was destroyed by a series of earthquakes that tore through the World's Edge Mountains. The dwarfs refer to it as the Time of Woe, as the dwarfholds were isolated and uncounted dwarfs died in cave-ins, fissures opening beneath their feet or entire sections of holds falling apart. The cause? On the other side of the Great Sea, a Slann Mage-Priest called Quex had realized the planet's continents had become slightly misaligned compared to the design documents left behind by the Precursors, and decided the time was right to re-align them.
- The Greenskin incursion at Grimspike Pass is an inversion. The Dwarf High King Kurgan Ironbeard marched his throngs out to meet the orcs. The newly appointed High Chief of Men, Sigmar Unberogen, gathered his warriors and moved to reinforce Kurgan's position, rather pragmatically counting on that their combined forces would have a better chance or repelling the orcs. Kurgan, in a similar bout of pragmatism, equipped Sigmar's warriors with steel weapons to replace the bronze or iron ones they brought, and gave Sigmar the rune-hammer Ghal-Maraz. From this simple act of Realpolitik grew an alliance which has lasted for over two millennia, and brought prosperity to both Men and Dwarfs.
- Warhammer 40,000: Inquisitor Fidus Kryptman. A radical even by Inquisition standards, Kryptman spearheaded a unique plan to deal with the Ork problem. Steal some Genestealers, implant them in some Orks and let the two forces wipe each other out. The problem? Neither seems able. The war in the Octarius sector rages on even in the current time of 40K, with the never-ending conflict making each side stronger. Whoever wins will either produce a Hive Fleet with an Ork WAAAGH worth of biomass, or an Ork force of immense size juiced up from all the fighting. Whoever does win, it's clear Kryptman's plan backfired big time.
- In the summer of 2008 on WWE Raw, CM Punk took advantage of a beating Edge received at the hands of a recently-drafted Batista to cash in his Money in the Bank contract, winning his first world title and ensuring RAW had a world title again. While that was great for Punk and everyone else on RAW, it was terrible for Edge and his associates, because Edge went into a complete Villainous Breakdown and started terrorizing his own show, WWE SmackDown, in retaliation. He did manage to collect himself briefly to finally get married to Vickie Guerrero, but then Triple H exposed Edge's affair with their wedding planner Alicia Fox during the wedding reception, causing Vickie to go into a Villainous Breakdown herself. She retaliated against Edge by reinstating The Undertaker and forcing her new husband into a Hell in a Cell match at that year's SummerSlam. After that and a poignant talk with Mick Foley (which saw Foley go through a table at Edge's hands), Edge effectively snapped and rampaged across SmackDown as an unhinged lunatic until he lost the match against 'Taker and was sent to hell for three months. In short, within five or so minutes, Punk managed to completely utterly wreck SmackDown for several months just by taking advantage of Edge's one vulnerable moment on RAW.
- Paige accidentally bumped into Summer Rae after winning a match. This act of disrespect caused the ring announcer to snap and attack Paige, thereby establishing herself as the new top heel Diva on NXT.
- Her actions would cause another Face–Heel Turn when she, as General Manager of Smackdown Live, booked Carmella in a match against Charlotte Flair in which if the latter won she would be added to the former's championship match against her friend Becky Lynch in retaliation to Carmella taunting her about never being able to win the Smackdown Women's Championship due to her Career-Ending Injury. This would lead to Charlotte winning the Women's Championship and Becky, feeling that Charlotte stole her spotlight, turning heel by attacking Charlotte thus destroying their friendship.
- Summer Rae later became one herself. She corrupted Sasha Banks in order to get an ally for herself and form the Beautiful Fierce Females. Little did she know that Sasha would become an even more effective villain than her - and eventually the NXT Women's Champion. Everything Sasha did as The Boss stems from that one "Reason You Suck" Speech. And for good measure, Ric Flair's daughter Charlotte, who they brought into the group early on as a stab against Bayley, has also advanced much further than Summer since then. As of summer 2016, Summer Rae essentially helped create the history behind the main feud for the WWE Women's Championship, and she herself has nothing to show for it.
- As Captain Henry Wirz testifies during the climax of The Andersonville Trial, General Sherman's march through and destruction of Atlanta only exacerbated the problems at Andersonville.
- Brand has Gerd, a Cloud Cuckoolander who crosses paths with the main character time and again, prompting his choices for the worse. At the end of the play, she is the one who fires the shot to loosen the lavine that buries the entire community completely (and everybody in it). Justified because she is obsessed by the thought of getting a shot at "the bad priest on the black peak". Whatever that is.
- Cyrano de Bergerac: Hilariously subverted by De Guiche: he is a villain who unwittingly derails his own plans. In Act I Scene IV, he utters a simple Dare to Be Badass to De Valvert, a small but crucial gesture that sets events in motion that result in the derailment of his own plan to marry Roxane to De Valvert so de Guiche could bully her to be his mistress.
- In Oscar Wilde's An Ideal Husband, the scatty Lady Markby brings a friend to a party, appearing in two scenes in the first act, and never appears onstage again. Said friend turns out to know their host's dirty secret, thus causing the events of the entire play.
- Into the Woods: After all the fairytale events, one of the consequences is that the widow of the giant Jack killed comes down seeking revenge against Jack. However, it's during the song "Your Fault" that the other characters learn that they were all indirectly responsible — the Baker was the one who gave Jack the magic beans in exchange for Milky-White, his wife attempted to give Cinderella an extra bean in exchange for her golden slipper, which she promptly threw away (it was this second beanstalk that the giant's widow climbed down), Red Riding Hood dared Jack to get the harp, which was the point where the giant became aware of Jack stealing their stuff, and the Witch was the one who raised the beans in the first place. All the other characters ultimately agree to blame the Witch for the whole thing — just because she's a witch and therefore an easy target — despite her being by far the least involved.
- In Jasper in Deadland, Virgil does a lot to impede Jasper from rescuing his friend Agnes. He's the first one to give Jasper a bottle of Lethe-brand water, which starts Jasper's memory loss and prevents him from recognizing Agnes and he later gives Jasper a fake death-manifest from Mr Lethe, saying that Agnes had entered Elysium and was most likely unreachable. Despite this, there's nothing to imply that Virgil knows that the death-manifest was fake or that the Lethe-Water causes memory loss - from his perspective, he's just giving someone a water bottle and a legal document. Virgil also seems genuinely happy when Jasper and Agnes get permission to leave Deadland.
- Miss Saigon: Ellen. Had she not reacted so badly to the idea of taking Tam, Kim might not have felt it necessary to kill herself in order to ensure that they would.
- The Zeroth Law of Trope Examples: Romeo's servant Balthasar in Romeo and Juliet, when he brings his message to Romeo telling him of Juliet's death. Sadly, the friar's letter telling him that the death was faked does not get through — so there are two Swiss Messengers, the one who delivers the wrong news, and the one who doesn't realize how important the real news is, and fails to deliver it. Actually seems to have achieved some degree of Pop-Cultural Osmosis, which runs counter to the norm for an author so prone to Common Knowledge.
- Sweeney Todd would never have gone on his murder spree as the Demon Barber of Fleet Street had Anthony not barged into his shop, with Judge Turpin right there in the damned room, in order to inform Sweeney of his plans to elope with Johanna, bombing both that plan and Sweeney's plan to kill Turpin straight to hell and making everything worse.
- Literally everything that happened in BIONICLE can be traced back to two characters' actions: Annona, who amplified the Great Beings' pre-existing compulsion to create, which eventually led to the Great Spirit Robot; and the Energized Protodermis Entity, who let the Core War happen and caused Spherus Magna to shatter. While it's debatable exactly how much of this was "unwitting", it's doubtful either of them foresaw just how much of an impact their actions would have.
- In DEATH BATTLE!, He-Man ended up as this during his fight against Lion-O. He just wanted to fend off Lion-O, but in doing so, he crushed the Eye of Thundera, which kept the Thunderian race alive.
- Llamas with Hats: In episode 7, Paul severs all ties with the series' Ax-Crazy Villain Protagonist Carl, as any sane person would. However, it turns out that Paul's friendship was the only thing keeping Carl a little bit sane (a very, very little bit), and without Paul around, Carl ends up destroying all life on Earth.
- In Red vs. Blue:
- It's revealed in season 10 that Carolina is the unintentional cause for multiple problems the cast faces in the Recollection trilogy, thanks to several ill-considered decisions regarding AI. Sigma was her original AI partner, but she felt guilty for Maine being rendered mute and gave Sigma to him to compensate. She then proceeded to demand the next two AI Fragments, Eta and Iota, to compensate (and because she was jealous of Tex for getting Omega, the strongest one). Eta and Iota were to be Wash and South Dakota's AI; when they were given to Carolina, Wash ended up getting Epsilon instead, leading to his mental breakdown, and South's envy of Wash and her brother (who had Theta) boiled over and ended with her leaving both of them for dead later (which would in turn lead to Wash killing her). Meanwhile, Sigma quickly gained complete control over Maine and used him to further his goals of metastability as the Meta. Carolina's rivalry with Tex also caused the events of Season 15- When she and Tex fought each other in a simulation, one of the Simulation Troopers with them was killed. His death (along with Carolina and Tex's uncaring reaction) inspired his best friend to rally both the Blue and Red teams to fight against both Project Freelancer and the UNSC for treating them so disposably.
- There's the Director's obsession with his dead love, Allison. When the Alpha AI, copied from the Director's mind, was created, the Beta AI (based on the Director's memories of Allison) naturally fragmented from it. This inspired the Director to torture the Alpha into making more fragments, the ones mentioned above, to figure out a way to "get her right".
- There is also the Sleeveless Insurrectionist Soldier, who shot Agent Maine in the throat several times, rendering him mute. This gave Carolina an excuse to give her A.I. Sigma away so that Maine could have an alternate way to speak. This contributed into forever turning him into the Meta.
- Season 14 ultimately reveals that The entire series happened because Agent Florida tripped over a wire and broke it. Originally, had something happened to him, other Freelancers were to show up and take his place, starting with Agent California. However, by damaging the wire, the list of Freelancers were replaced by those of normal Simulation Troopers, beginning with Caboose and Donut, who would trigger the plot. Thus, because of a damaged wire, Agent Florida would kick off a series of events that would lead to the destruction of the Freelancer Project.
- RWBY: Flashbacks depict Cinder living in an abusive environment where she works as a slave for the hotelier who is her legal guardian. When she steals a customer's sword to kill her abusive family, he decides to give her a legal escape by training her to become a Huntress. When Rhodes gifts Cinder with a twin of the weapon she once stole, her step-sisters finding it triggers a confrontation that snaps Cinder. Thanks to years of training and torture, she kills both her family and Rhodes, beginning her journey of killing others to steal power for herself; this leads her right into Salem's arms, earning her a major role in the Secret War with Professor Ozpin for the fate of humanity.
- Supermarioglitchy4's Super Mario 64 Bloopers: In "Mario Saves Anime", Fishy Boopkins explains to Francis that Axol's inkweaver uses inkling ink to bring anime drawings to life. This would soon result in Francis kidnapping most of the population of Inkopolis, including Meggy so that he could have his own island of waifus. This also results in the death of Desti after False Sephiroth impales her.
- Cobra Kai would have an easier time listing aversions. The second season ended up with the campus equivalent of a Mob War (and one student on each side hospitalized).
- Trouble in Dino Attack RPG, being a mutant lizard who was adopted and trained by a member of the team trying to eradicate his kind, was the first to spark the tension between realist and idealist members of the team. Technically speaking he is responsible both for the campaigns by both Kotua and Cam O'Cozy, both of whom tried to commit genocide against idealist agents.
- Don't Hug Me I'm Scared:
- Red Guy is heavily implied to be this in the fifth episode. At the beginning of the episode, Duck Guy and Yellow Guy note that something's "missing", unaware that it's their friend Red Guy. Near the beginning of the episode, a phone rings, and when Duck Guy answers, he's suddenly in an operating room, watching himself on the television, with a mysterious voice saying "you have to know right from wrong". This seems to lead him to realize that the lesson would go wrong somehow and try to escape, for which he is Eaten Alive. The end credits imply that the call was made by Red Guy, who somehow escaped from the lessons and was trying to help his friends escape, and hearing Red Guy's voice was what made Duck Guy realize what was going on. If it weren't for Red Guy, Duck Guy would probably still be alive, and Yellow Guy wouldn't be completely alone.
- The sixth video takes this further by implying that Red Guy is somehow inadvertently causing the "Groundhog Day" Loop the puppets are trapped in.
- The Dream SMP has Quackity, who — after being told they'd be the only party running — decided to run against Wilbur and Tommy in the L'Manburg Presidential Election. This opened the gates for other people to form political parties to run against Wilbur and Tommy... including Jschlatt, who wound up pooling his votes with Quackity's in order to win. Immediately after becoming President, Schlatt declares himself Emperor, exiles Wilbur and Tommy, tears down major landmarks, and starts crushing any dissenting voices hard.
- In late Season 4, Kary commits the Innocently Insensitive act of choosing to check out an in-game event over finishing her (in-game) wedding to Arthéon, who was taking it much more serously than she was. Arthéon was so furious that he went on a Roaring Rampage of Revenge. Even after he calmed down, he still had a much more cynical view of everyone and everything he knew than before. This became a really bad thing because Arthéon eventually got a job that enabled him to impact the game's plot and the story has reached a point where he will be responsible for the game world's destruction unless his former guildmates stop him.
- In late Season 5, Roxana keeps Saphir from doing a quest that impacts the game story and may have the side a effect of making Saphir's guild outrank Roxana's once it's done. The reason the quest could have been singlehandedly enough to significantly uprank Saphir's guild? It would bring a big blow to the Big Bad if accomplished, help make him stronger if failed.
- In SCP Foundation, SCP-1867 ("A Gentleman") is Lord Blackwood, an adventurous seaslug who appears in many other works telling about his adventurous times. If the accounts are correct, Lord Blackwood may have just been the one that inspired SCP-319's maker to try and travel to another universe, and gave him the means to attempt it. A short read of that particular file lets us know that attempt essentially doomed this universe.
- The Tim Tebow CFL Chronicles: Tim Tebow unintentionally destroys Canadian football. Unknown to him, the rest of the league can't start the 2014 playoffs until they get the results from his game against the REDBLACKS. But with Tebow leading the Argos' offense, and with the utterly bizarre rules of "bound-for-street" play, the game lasts over a decade—while every other team can't do anything but wait.
- In Worm, the Undersider's local Smart Girl, Tattletale, normally isn't this, but a character flaw of hers is to start throwing everything her Sherlock Scan superpower picks up everywhere when she panics. This doesn't really hurt anyone...with the rather glaring exception of cluing Panacea into her family history...which sets off the time bomb of issues that is her adopted family, and ends with Panacea's incarceration and her sister becoming a miserable pile of immobile flesh.