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Unwitting Instigator Of Doom / Live-Action TV

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Unwitting Instigators of Doom in live-action TV.

  • Agents of S.H.I.E.L.D.: Way back in the ancient past, some Kree scientists decided to perform experiments on a bunch of primitives on a backwater planet to create expendable troops for their empire. The experiment was deemed unsuccessful and the Kree left. Thousands of years later, that minor experiment led to essentially everything that happened, good and bad, in the Marvel Cinematic Universe.
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  • In The Andromeda Strain, the satellite containing the eponymous plague crashes near two teenagers who decide to pick up the satellite and bring it back to town where it is opened by the clueless and curious townsfolk, which unleashes the plague and decimates the town. Had the military actually gotten to the satellite first, they planned to open in a much more secure location, averting the crisis.
  • Arrow:
    • One day, a young thug named Danny Brickwell was undergoing his initiation for a gang in the Glades. The initiation process required him to kill someone to get in. He chose a brunette woman who ran the free clinic there. That woman? Rebecca Merlyn. After that, it was just one domino after another.
    • Moira Queen is the indirect cause for the events of Season Three. During the events of Season Two, prior to her death, she informed the League of Assassins of Malcolm Merlyn's survival. The League, specifically Ra's al Ghul himself, were not happy with Malcolm after the Undertaking, and marked him down for death. Malcolm became so desperate to get off the League's hit list that he went as far as to brainwash Thea, his own daughter, into killing Sara Lance, and taping it to blackmail Oliver into accepting the blame for Sara's death and issuing a challenge to Ra's al Ghul — by killing Ra's, Oliver would be able to get everyone, even Malcolm and Thea, out of the red.
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  • Band of Brothers has Dick Winters and Moose Heyliger deciding to take a stroll one evening just to check on the men's morale. A sentry mistakes them for the enemy and shoots Moose. This results in him being pulled off the line and the incompetent Lt Dike is put in charge of Easy Company - just in time for the horror of Bastogne and the Battle of the Bulge, during which many men lost their lives. The sentry in question was quickly transferred to another regiment for his own safety.
  • The Barrier: The criss-cross between the various plotlines involving the protagonists results in acts that should have only affected one plotline on paper end up having negative knock-on-effects the person comitting them couldn't have predicted:
    • Julia is pretending to be her dead twin sister Sara half to hide from the Police State, half because her brother-in-law Hugo needs Sara to be alive to keep a job. The police eventually takes Julia in for interrogation as Sara, and Hugo insists on going with her. This happens while Hugo and Julia's employer Luis is visiting Julia's mother. With Hugo away, Luis is driven home by Hugo's brother Álex. By that point, Álex has met a few members of La Résistance, including a Rich Kid Social Activist who lives in the same area of town as Luis. Of course, Álex being Luis' driver instead of Hugo results in him finding out who the resistance member is in real life.
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    • Julia's legally dead boyfriend Carlos breaking into the room used by Hugo's daughter to drop off an item he wants Julia to find results in Hugo getting worried enough about his daughter's safety to bring her to work with him. One of Hugo's employers spent time using his daughter as experimental subject, and the girl being in their house allows for the experiments to continues without Hugo being the wiser.
    • An acquiantance of Hugo's and Julia's employer dying via an implied assassination results in the employer's orphaned nephew being underfoot during the aftermath. Hugo and Julia take the nephew to their home so they can watch him on his time off, but people leaving in the same area turn out to be the boy's biological family that had him taken away under false pretenses. The consequences of the discovery ultimately get the the boy's biological parents killed.
    • One of the recurring policemen takes a specific subordinate along with him while evacuating a camp containing a large number of Legally Dead children. One of the children is the subordinate's own son, and the boy's mother has been meeting up with a group of parents in the same situation of them. The subordinate himself, however, has up to that point been extremely skeptical of the group's claims.
  • Brave New World: John's mother arranges to have him sent to New London to have the life she believes he deserves. Once in their society it's shown that his very presence and refusing to conform with their society's norms is causing them huge problems.
  • Breaking Bad:
    • Hank Schrader just wanted to show his brother-in-law about a basic day at his job. He accidentally ended up creating Heisenberg.
    • Walt letting Jane die causes her father's deep depression which he worsens when he accidentally causes a mid-air collision leading to deaths of hundreds of people.
    • Similarly, Walt's Alcohol-Induced Idiocy when he could have let Gale take the fall for being Heisenberg bites him really hard when Hank fully devotes his resources into investigating Gus, which Walt desperately tries to avoid by causing an accident which almost kills both of them.
    • Jesse's insistence on revenge regarding the murder of his girlfriend's brother leads to Gale's death after Gus deems Walt dangerous, which leads to Brock getting poisoned, Gus's death and his business collapsing, as well as Mike's death.
      • Jesse returning to confront Walt after he finds out Walt poisoned Brock causes Hank and Gomez's deaths, Walt's family getting permanently fractured, his own enslavement at the hands of Uncle Jack's gang, and Andrea's death at the hands of Todd after Jesse tries to escape.
    • Skyler giving away Walt's money to Ted to cover their tracks leads to Walt's emergency plan to poison Brock to bring Jesse back to his side and kill Gus.
    • Gale's involvement in Pollos Hermanos becomes this as he is killed by Jesse, his trail makes Hank investigate Gus which leads to his death, as well as Gale's gift to Walt busting him at an inopportune moment.
  • Buffyverse:
    • Wesley in Buffy overheard that Faith accidentally killed someone. The rest of the team is already on-board with helping her deal with her issues and giving her the support and acceptance she needs in order to not fall to The Dark Side. Wesley's response on the other hand is to call in some goons and try to ship her to England to be locked away forever. By the end of the episode, she doesn't trust any of them, resents all of them (because she thinks they want her to just be like Buffy), and has taken a job as the Big Bad's number two.
    • Angel. Wolfram & Hart has a stated mission of bringing Angel to their side. Sound pretty far-fetched? The road to Hell is paved with good intentions.
  • A particularly heartbreaking episode of Cold Case gave us a girl who had a crush on the Victim of the Week, who was a mentally-challenged teenager. One day alone in class, she tried to kiss him when her meathead boyfriend walked in and she lied and said he tried to sexually assault her so that she wouldn't get a "bad reputation", which essentially caused him to be beaten up by the said boyfriend and his gang of thugs (as well as his only friend, who was embarrassed by him), her parents deciding to file charges against him, him ending up in an institute instead where, due to his alleged sexual deviance, is in the worst tier of the facility where the care for the patients is horrifyingly neglectful, quite frankly. In addition to this, the boy's loving mother (and one of only two people at this point who gave a damn about him) is dying of cancer as all of this is occurring, the boy's father won't take care of him because of his mental status and the boy's caregiver, who was also dating the mother, takes him from the institute and rather than have him live a life of loneliness and neglect, has him run over by a train. In present day, the girl FINALLY realizes the effect of her actions and is remorseful, but it's still too little, way too late.
  • Control Z: It turns out that Sofia actually gave the hacker the idea for exposing everyone's secrets with a comment she'd made.
  • In the second season of Criminal Minds, the team was trying to bring in a delusional war veteran who is panicking because the construction sounds like the war zone. Now, they find him and have swat surround the suspect as they coaxed him to surrender. They tell these construction men nearby in plain view of the drama to stop working until they are done, but naturally the men resume construction before the suspect is apprehended. This causes the suspect to panic and he runs towards a kid on a bike, forcing a SWAT marksman to shoot him.
  • Curfew:
    • A flashback shows that Kaye Newman was involved in the experiments that led to the mook virus. At one point, she visits the lab and finds it overrun with the mutated test subjects. Following a soldier's instructions, she fills the lab with nerve gas and kills the test subjects, only to find another managed to escape the building. When she sees he's another of the researchers who became infected, she can't bring herself to shoot him and he runs off to cause the outbreak. This leads to England becoming a police state, the titular curfew, and the race.
    • Possibly one of the sillier examples of this occurs in episode eight. After Meg catches Cheese trying to pour soda into her team's gas tank, she gets him to back off at gunpoint. A couple of others join in and a Mexican Standoff occurs. Meanwhile, El Capitano takes the soda from Cheese and drinks it himself. While the others are tensely pointing their guns at each other, El Capitano burps and triggers a shootout. Meg, Zane, and possibly Lou Collins die from being shot and the noise attracts the mooks (who kill the biker), forcing everyone into the building (except Lou and Hanmei who take off).
  • Degrassi: The Next Generation gives us Paige Michalchuk, who gets her friend Terri drunk before a dance and ends up with the guy Terri wanted instead. Later on, Terri thinks she'll never find a man and ends up with abusive boyfriend Rick. Later, Rick comes back and Paige gets to be an inversion of this trope, albeit ultimately subverted because someone else pisses Rick off enough that he starts shooting people.
  • Doctor Who:
    • "Partners in Crime" has a minor example — Donna unwittingly causes Stacey Campbell's death by fiddling with the Adipose Industries necklace she stole. This causes an Adipose to be created from Stacey's fat cells out of schedule, which she witnesses, leading the company's head, Miss Foster, to convert the rest of her into Adipose in order to hide what the company is doing.
    • "The Waters of Mars": When the Doctor realizes he's at Bowie Base One, the first human outpost on Mars, which is destined by a fixed point in time to be destroyed with all its crew, he tries to leave immediately. The base commander, Captain Adelaide Brooke, suspicious of him, prevents him from leaving... thus nearly leading to a Time Crash before Adelaide has to kill herself to reassert the timeline.
    • "Resolution": In 9th century Yorkshire, several bandits shoot and kill a man riding south before leaving his body in the road. Unbeknownst to any of the thieves, the man was a custodian of one of three pieces of a Dalek recon scout which had come to Earth, and his murder leaves the piece unguarded. 1200 years later, this leads to two archaeologists digging up the piece and accidentally bringing the creature back to life...
  • In an episode of the The Drew Carey Show, Drew accuses Mimi of playing more pranks on him than usual, but insists that what ever's been happening is not her doing. The security guard then shows Drew footage from the store's cafeteria where three employees sing about how much they hate him. When Drew confronts them about the pranks they reveal that it's pay back for something he did to them. One employee was up for a promotion, but when Drew repeated a joke he made about the boss' toupee, the boss comes into frame and demoted the employee. Another employee said that he wanted to smooth things over with his girlfriend, but after Drew, who was eating BBQ ribs, straightens the employee's shirt it makes it seem like he had lipstick on the collar, and she dumps him. The third employee was mad because Drew reported him for drinking on the job, and he was still drunk while Drew was talking to them. After things get straightened out, and Drew apologizes for what he did, a glass worker calls his wife who's threatening to divorce him that he will be home soon after he finishes installing a panel in the door of Drew's boss, which Drew accidentally breaks, and jokes that glass worker has to work overtime. The next day, someone plays pranks on Drew.
  • Farscape: In the first season episode "A Bug's Life", Rygel and Chiana inadvertently cause all the subsequent major events of the show to happen by opening a box. They assume it contains something valuable they can steal; it actually holds the host for a sentient virus which gets loose aboard Moya, setting off a chain of events which lead to Aeryn being critically injured. In order to save her life, in the following episode the crew have to go undercover on a nearby Peacekeeper military base to acquire the tissue samples necessary for her surgery. Unfortunately Crichton arouses the suspicions of the base's commander, Scorpius, who subjects him to a Mind Probe and discovers that Crichton's brain contained the information necessary to create wormholes — which happens to be exactly what he has been seeking for years, as it would provide not only near-instantaneous travel to any point in the universe, but could also be used to create a devastating weapon. Scorpius' single-minded determination to acquire the information from Crichton's mind drives the plot for the rest of the show.
  • The Flash (2014):
    • Subverted with Harrison Wells in Season One. Initially, it's played off as though the particle accelerator explosion in the pilot was a complete accident (which would be this trope). However, eventually, after the revelation that he is in fact secretly Eobard Thawne aka Reverse Flash, we end up learning that he intentionally created the explosion in order to give Barry Allen his speed and create Flash's famous Rogues Gallery in order to eventually have Barry go back in time so he could return to his time period.
    • Played straight in season six with Nash Wells. He becomes so desperate to get revenge on the Monitor that he ignores how convenient all of the events that lead him to Earth One are, and ultimately release the Anti Monitor from his prison and unleash an antimatter wave on the multiverse, thus causing ''Crisis on Infinite Earths (2019).
  • Game of Thrones:
    • Robb's infatuation with Talisa results in the Freys, Karstarks and Boltons breaking with House Stark, leading to the extermination of the Starks and their loyal bannermen at the Red Wedding.
      • Being rude to Tyrion when he returns to Winterfell after visiting the Wall makes Tyrion decide to go stay at an inn instead. When he does, he comes across Catelyn, who impulsively arrests Tyrion because she mistakenly believes he attempted to kill Bran, and takes him to the Eyrie, thus kickstarting the Stark vs Lannister feud.
    • By never going public with the Mad King's plan to destroy King's Landing with wildfire, Jaime left the door open for Cersei to eventually find and employ it herself. Hundreds if not thousands of people died along with a good chunk of the city, all because he kept silent.
    • Tytos Lannister was too weak-willed and too nice, which brought House Lannister to near ruin and drove Tywin to become a strong and ruthless leader, which caused even more problems.
    • As revealed in the Season 7 finale, Rhaegar Targaryen and Lyanna Stark really fell in love with each other; however, they secretly married somewhere without bothering to tell their families and other parties concerned about it. As a result, many people believed that it was an abduction which led to the deaths of Lyanna's father and oldest brother and an open rebellion led by Robert Baratheon culminating to the many deaths, the exile of the remaining Targaryens from Westeros and a long enmity among the houses affected by the war, namely Houses Lannister, Stark, Baratheon, and Martell.
    • His Caligula tendencies aside, Joffrey's insistence on trying to embarrass Tyrion just before he died of poison provided the perfect excuse to blame Tyrion of the crime, since he quite literally put the poisoned goblet in Tyrion's hand. This in turn leads to the complete upheaval of local politics when his mother badly mishandles things and drives Tyrion into the employ of Daenerys, which the various houses of Westeros will no doubt regret when she makes her way back.
    • Tyrion Lannister:
      • His murder of Tywin had unintended and terrible consequences. Though utterly ruthless, Tywin had been the primary force keeping Westeros in a state of (fragile) peace. Worse, his death gave Cersei free reign and allowed the Sparrows to move on King's Landing, setting off a chain of events ending with thousands dying in a Wildfire explosion and Cersei sitting on the Iron Throne.
      • Tyrion, like Jaime, knew about the Wildfire caches buried underneath King's Landing and multiple monuments. During his time as Hand, he used some of it at Blackwater but left the rest where it was underneath the city, ready for someone to use it. By failing to report or act on his knowledge, he is culpable in Cersei's atrocity.
      • His demand of Trial by Combat indirectly results in the deaths of several characters, not counting the ones he killed himself. Oberyn Martell dies in the fight, which leads to Ellaria Sand's attempt at a Roaring Rampage of Revenge. This ultimately results in the deaths of Doran Martell, Trystane Martell, Areo Hotah, and Tyrion's own niece, Myrcella. (Eventually, the Sand Snakes, in an attempt to get this revenge, throw in their lot with Daenerys Targaryen which results in all four of their deaths.) Also, it allows the Mountain to reach the dead/near death state necessary for Qyburn to experiment on him, creating an arguably stronger and nastier zombie-Mountain to serve as Cersei's muscle.
      • In Season 7, Tyrion's plans backfired immeasurably on his allies: his strategy to have King's Landing being captured by their Westerosi allies while the Unsullied take Casterly Rock leads to the Greyjoys and the Dornish leaders being taken out, the Unsullied trapped inside a empty Casterly Rock whereas the bulk of the Lannister army sacked and destroyed House Tyrell, effectively robbing Daenerys of all her allies from the continent. His suggestion to bring a wight South and show it to Cersei in order to propose a truce between their enemies lead to the death of the only Red Priest in Westeros and the White Walkers gaining a dragon and using it to breach the Wall, all for practically no gain since Cersei has backed out from the propose alliance.
    • Varys's actions have probably done more to bring Westeros and Essos to its doom than even Littlefinger's witting instigation of chaos:
      • His insistence on selling Dany to Khal Drogo started a series of Disaster Dominoes that led to the cooling of the friendship between Ned and Robert; the assassination attempt on Dany led to Khal Drogo and his khalasar murdering the Lhazareen; this leads to Drogo's death, which splits apart the Dothraki into warring factions; and to Dany hatching her dragon eggs in Drogo's funeral pyre, which leads to the birth of her three dragons.
      • His decision to support the Lannister regime in Season 2, just to prevent Stannis and Melisandre from taking over, leads the corrupt Lannister regime to assert its dominance, as a result of which Westeros becomes a chaotic despotic regime ruled by Cersei Lannister who plunders, robs, and murders her supports creating a regime where the likes of Euron Greyjoy and the corrupt Iron Bank are in charge. Likewise, by hampering Stannis' campaign, he damaged the only candidate of Westeros who could have peacefully resolved the War of the 5 Kings and rallied Westeros for defense in the Long Night, since Stannis' attempt to aid the Night's Watch and rescue the North from the Boltons collapsed because of a lack of support, and Jon Snow is meaningfully hampered in trying to pick up where Stannis left. Much of this could have been avoided had it not been for Varys.
    • House Greyjoy's invasion of the North and Theon's raid of Winterfell not only disrupted the Stark supply lines in the War of the Five Kings, but demoralized Robb and helped convince Roose to betray him. If the Ironborns had stayed out of things, the war may have gone quite differently.
  • In murder mystery Harper's Island, nine-year-old Madison is kidnapped by the Ax-Crazy Big Bad, John Wakefield. When rescued, she goes along with the lies Wakefield told her to tell the others — specifically that it was the Sheriff who kidnapped her. Even though she knew that Wakefield was evil. This gets several people killed.
  • In House of Cards (US), President Garrett Walker promised to make Frank Underwood his Secretary of State in exchange for Frank's help in the 2012 election. After it was over, Walker reneged on his promise, causing Frank to seek revenge. Revenge that entails multiple murders, ruining the lives of any number of people, and finally Frank stealing Walker's presidency out from under him. And that's just what Frank does to get to the Oval Office. Once there, he firmly establishes himself as a President Evil that puts his own ambition before the needs of the country.
  • The InBESTigators: When Pixie nearly catches Amelia on her phone in "The Case of the Sleepover Secret", Amelia apologizes and then not wanting to admit what she was actually doing, says that she's sorry about Pixie's parents getting a divorce. She had no idea that it was a secret until Pixie snaps at Ava about supposedly sharing it.
  • Kamen Rider:
    • Emu Hojo/Kamen Rider Ex-Aid is the sweetest one out the Doctor riders and overally one of the nicest people in the series. Unfortunately, this causes a messy chain of events more than once. He sent fanmail to his idol. This pushed said idol of the deep end and kickstarted the series's events. He was a lonely child and wished for an Imaginary Friend. This wish materialized as Psychopathic Manchild Enemy Within / Enemy Without Pallad. This, along with many other things, makes him one of the most tragic Kamen Riders of the franchies.
    • This also happens in Kamen Rider Gaim in the form of Mai Takatsukasa as the Woman of the Beginning. After being turned into an Overlord, she attempts to use her newfound powers to travel back into the past befor everything went to hell in order to convince Kouta, Mitsuzane, and Kaito to abandon the battle. Unfortunately, because she didn't know how to use her powers properly she was only capable of Vagueness Is Coming messages. Her actions only pushed her friends into fighting a brutal war.
  • Law & Order: Special Victims Unit:
    • In one episode, the detectives are investigating the rape and murder of a woman who fled her abusive husband. They find that she was working as a stripper and quit after recognizing one of her neighbors as a customer. Said neighbor promptly told her husband, unaware of what kind of man he really was, and the man tracked his wife down and killed her.
    • In another episode, a famous rock star expresses anti-psychiatry and anti-medication views in a TV interview, causing a bipolar teenager to stop taking her medication. This leads to her falsely accusing two boys of rape, getting them and herself expelled from school, and trying to kill herself in a car accident which leads to six people getting injured and another girl dying.
    • Another features a blowhard radio pundit, played by Lewis Black, who had a running feud with an actress who played a Ms. Fanservice role on a TV show, and would often rant about how she's "asking to be raped." The episode's plot is kicked off when a teenage Loony Fan of the pundit actually goes and does it, prompting a huge debate about culpability and free speech among the characters. The episode ends with the pundit being shot, albeit nonfatally, by the rapist's vengeful mother after the rapist is convicted.
  • Malcolm in the Middle:
    • In one episode, when Hal, Abe and his friends were going to take part in a local talent showcase, Dewey asks Hal, "Why are you always in the back of the group?" Which soon leads to an argument over whose the better musician, and they attend the show, but refuse to participate. During the show, when Dewey congratulates a young couple for their routine, he asks "how come you dance a little bit faster?" As Dewey watches the show, the couple is seen in the background having a heated argument. After Hal and the rest the group decide to put their differences aside and perform, one of the members says "party at my house!" and the rest cheer, until Dewey asks "How come the parties are are always at your house?"
    • In another episode, Francis and Pyama are arguing about their finances, but decide to stop before it gets out of hand. Later Francis asks Otto, his boss, if he's ever argued with his wife over money. They get into a big fight. After they make up, Otto asks a guest at the dude ranch if they argue over money, cue heated argument. Throughout the episode, couples can be seen and heard in the background arguing over money. At the end of the episode, someone calls the front desk, manned by Francis, from Australia and informs that their reservation is cancelled. When Francis asks why, the caller asks Francis if he and his wife have fought over money. Pyama comes into frame, and Francis, with an angry look on his face, excuses himself and hangs up.
  • Hilariously and perfectly summed up in the Married... with Children episode "976-SHOE" where Marcy yells at Steve for his boneheaded decision to loan Al $50,000 from his bank for an unsuccessful shoe hotline to win an office sweepstakes contest to Hawaii:
    Marcy: You loaned this man $50,000?! That's $1,000 an I.Q. point, and I can't really blame Al; after all, if you give a gun to a chimp and then the chimp turns around and shoots someone, you don't blame the chimp!
  • An episode of Medium has Allison herself as this. A series of serial killings are revealed to be the work of someone she knew when they were teenagers. The killer was going to kill himself once, but Allison came over to his house to talk to him and interrupted his attempt. Fortunately, this episode features Mental Time Travel to when they were teenagers. This time, Allison doesn't interrupt his suicide attempt and lets him kill himself, thus preventing the killings from taking place.
  • Narrowly averted by Princess Mithian on Merlin, who, in a bid to impress King Arthur, shoots a young deer in the forest. Unbeknownst to her, the deer is actually Guinevere under an enchantment. Only Merlin realizes what she's done and returns to the forest at night to hunt for Gwen and heal her from her injury.
  • Once Upon a Time:
    • Baelfire is one of the main causes of the plot in the show. His father Rumpelstiltskin became the Dark One to protect him from becoming a child soldier. His disappearance into another world is what caused Rumpelstiltskin to search for a land without magic - and so create a curse dooming the entire populations of multiple worlds to years of misery. All of Rumple's deals and schemes, including turning Regina Mils into a "monster," was part of his plan to find Baelfire.
    • Also, Queen Eva started the bitter and long feud between Cora, Regina and Snow's family because when she was young and a Spoiled Brat, she exposed Cora as an unwed mother to keep her fiancee King Leopold from marrying her. Then she tripped Cora, claimed that Cora hurt her, and thus began Cora's long vendetta against the nobles and in particular, her family.
    • Likewise the palace gardener Jonathan pretended to be the prince, and seduced Cora while she was working in a tavern. Thinking they would marry, she slept with him and got pregnant with Zelena, the Wicked Witch of the West.
    • In the first season finale, Jefferson decides to get revenge on Regina by exploiting Rumpelstiltskin's love for Belle. In doing so, Rumpelstiltskin sends the Wraith against Regina in his own revenge which results in it (along with Emma and Mary) to be banished to the Enchanted Forest. The following events led to Cora finding her way to the real world and set off almost all the events of Season 2, and by extension, the rest of the series.
    • Mr. Gold's pursuit for revenge at the end of season 3 winds up severing the ties with that arc's Big Bad and her Amplifier Artifact. This results in the magic triggering her Time Travel spell which got Emma and Hook trapped in the past where they, along with several other things, end up bringing with them a golden urn that spills over, leading to the release of Elsa and the first half of Season 4's plot.
    • The season 4 crossover arc with Frozen (2013) is another case, according to the episode "The Snow Queen". Basically, the Duke of Weselton tried to seduce his betrothed Helga's sister Ingrid. This caused Helga to be killed by Ingrid, which causes Ingrid's other sister Gerda to develop a fear of her family's magic, which led to her and her husband seeking to find a way to treat Elsa's magic, and caused the events of the movie to happen and the events of the Frozen/OUAT crossover to happen.
    • In a way, Rumpelstiltskin's pursuit to sever his ties to the darkness that binds his heart in Season 4 is what leads to Season 5. Eventually the heroes get the darkness out of him, but said darkness decides to get a new host, Emma. This results in the Dark Swan arc which, because of a long chain of events, ends in the Underworld Arc.
  • Halfway through season 3 of Person of Interest, Simmons kills Carter in revenge for the fall of HR. This causes Reese to go into a 10-Minute Retirement, requiring Fusco to track him down and drag him back to New York. This leaves Team Machine critically understaffed during their next case, while allows Decima to get a hold of the source code of the Samaritan AI, which would become the Big Bad of the next two seasons. That's right: a revenge murder by a Dirty Cop at the wrong moment nearly caused the entire world to be taken over by an evil supercomputer.
  • Power Rangers:
    • Power Rangers RPM: To escape from the research facility she spent most of her pre-series life confined to, Doctor K decided to release a sentient computer virus her captors had made her design for them. She intended to keep it to the facility's computers, but two guards caught her before she could finish installing the firewall, ignoring all her protests. Cue the destruction of human civilization outside of Corinth City.
    • Due to a lot of Time Travel and Anachronic Order being involved, the Blue Senturion in Power Rangers Turbo is often accused of being this, the negative result being Zordon's death. He'd come back in time a thousand years to warn of a massive war a year later — but the villains intercepted him, took the message, then wiped it from his memory, resulting in the evil side of the war being way more prepared than the good guys.
      • Of course, time travel being what it is, no one really knows how different the end result would have been.
    • In Power Rangers Dino Charge, Keeper tricks Fury into retrieving the Energies for Sledge, only to find that Keeper swapped the Energems with his crystal bomb. It causes Sledge's ship to drift into space and his asteroids to fall to the earth, causing the extinction of the dinosaurs.
  • In the BBC's Robin Hood the titular character is trying to make a tentative alliance with Isabella, the new Sheriff of Nottingham (and his ex-girlfriend) despite the grumblings of the other outlaws. His reasoning is sound, and after striking a deal with her he asks Little John to escort her safely home. For no reason whatsoever, John decides to tell Isabella that Robin "has eyes for Kate" (a fellow outlaw). This achieves nothing except pissing Isabella off and leading her to doubt that she has any kind of power over Robin. She turns on him at the next available opportunity which leads directly to two outlaws' deaths. Nice job antagonising the valuable ally, John.
  • Octavia in Rome may have been indirectly responsible for the deaths of Julius Caesar and Vorenus' wife. Octavian told her about Vorenus' wife's affair and told her it was a secret. For no reason whatsoever, Octavia told Servilla this. When Caesar's enemies planned to assassinate him, this information became crucial and was used to drive Vorenus (who was supposed to guard Caesar) away, leaving Caesar as a sitting duck. Meanwhile, Vorenus confronted his wife and she ended up killing herself out of honor. And of course, there is the whole second round of war and murder until it is settled who succeeds Caesar, which ends with the establishment of The Empire.
  • Valerie in the Sabrina the Teenage Witch episode "Sabrina and the Beanstalk". She decides to phone Sabrina to ask about shampoo, which makes Sabrina forget she was supposed to pick up spell ingredients from the Other Realm. When she gets off the phone, the store is closed, so Sabrina substitutes the ingredients for magical jumping beans. When they don't work, she throws them out and a beanstalk grows in the backyard. What's more is that Harvey eats one and gets sent to the top of the beanstalk - where he bumps into a Wicked Witch (apparently the Wicked Witch) who likes to eat mortals.
  • In Seinfeld, George does this multiple times. In the Pilot arc he, among other things, causes Crazy Joe Devola's multiple attempts on Jerry's life when he comes crawling back to NBC willing to accept less money for the pilot script after rejecting their initial offer, unknowingly undercutting Devola's writing deal with them.
    • Kramer becomes this in the Grand Finale when Jerry and George's Show Within a Show finally gets a season pickup, and the four main characters are taking a private jet to Paris for one last hurrah. He boards the plane with water in his ears from a trip to the beach and falls into the cockpit while trying to knock it out, nearly causing the plane to crash. Instead, the pilot manages to land safely in a small town in Massachusetts, where the four witness a carjacking and get arrested due to a local law holding people accountable for Bystander Syndrome, eventually being forced to spend a year in prison.
  • Star Trek:
    • In Star Trek: Deep Space Nine Kai Opaka gives Commander Ben Sisko one of the Tears of the Prophets and asks him to find the Celestial Temple to help reunite the Bajoran people. What she didn't realize was that the Celestial Temple was actually a wormhole to the other side of the galaxy. Its discovery by the Federation led to disastrous first contact with the Dominion and eventually the most devastating galactic war of the Trek verse.
      • Then again, that war led to the further entrenching of the alliance between the Federations and the Klingons, a revolution against the Cardassian military leadership, peaceful relations with the Romulans, and internal reforms in the Dominion. In the long run the galaxy may be better off, but at what cost?
    • Star Trek: Picard: The fourteen worlds that threatened to secede from the Federation got their wish of having the rescue mission for Romulus abandoned, but by doing so, not only did this result in Picard resigning from Starfleet, but also Nero's Start of Darkness that led to him unintentionally creating the Kelvin timeline.
  • Veronica Mars:
    • At Shelley Pomroy's party, Madison Sinclair was given a drink she didn't want, so she spit in it and gave it to Veronica. She didn't know that the drink was dosed with GHB which led to Veronica getting raped. When Veronica blasts her for it, she still doesn't see how it's her fault.
    • During a debate for the election for sheriff, Don Lamb accuses his opponent Keith Mars of being this for the recent bus crash. As a beat cop, Keith once pulled over the bus driver for DUI but let him go. It later turns out that the bus driver was innocent of the crash. In a bit of subtle irony, Lamb himself is the Unwitting Instigator of Doom because if he had investigated Veronica's rape, he could have arrested Cassidy Casablancas before he could trigger the bus crash.


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