Erma's father Kanoc is this for her: Haven't he being tortured to insanity by the ILR, Erma wouldn't never have the motivation to join the EDFnote Albeit Erma already wanted to join the EDF, regardless of what had happened with her father anyway., she could have remained a Fake Cutie and a Jerkass for the rest of her life, jeopardizing any attempt to join the EDF later, something The Net itself makes painfully clear to Erma later on and very possibly he, Erma and the rest of the Felnas could have died during the ILR attack to their homeworld.
Erma's former boyfriend Tavas Ikalik, big time: Tavas was an ambitious but run-of-the-mill pilot who had a hot girlfriend (Erma), and a good life behind them. Had Tavas hadn't tried to convince Erma not taking part of the Battle of Derzon and simply had he left the whole thing peacefully, he wouldn't had become so vindictive against her, he wouldn't had convinced the EDF on sending Erma to Ekosiak, and very probably, the whole events on the ILR attack on Dornthant had occurred in a very different fashion.
In the Chick Tract "Fatal Decision", Brutus, an orderly on the brink of being fired for rudeness to patients, makes hints that John shouldn't trust Dr. Bowers, leading to John destroying the vaccine and dying of his disease.
The devils often invoke this trope, choosing someone who has an incidental relationship to the person whose soul they want to claim. In "The Assignment" they succeed in convincing Charles Bishop's subordinate's wife to badger him out of witnessing to his boss. They try to distract Cathy with a boy, only for it to fail when he proves to be a Jerkass, and try to have the previously mentioned subordinate call Bishop with a sales proposition, only for the angels to thwart this attempt twice. Charles ultimately dies in his sins, making the first example a successful one.
Many people in Eight Billion Genies don't intend to cause harm with their wishes, but their ill-thought out wishes or acts as a result of those wishes cause enormous carnage and destruction. One person who wishes for a lightsaber accidentally starts a fire that engulfed all of downtown Detroit. As one of the genies notes, she asked for a lightsaber, not how to use it.
Irredeemable: In a broad sense, Daniel/Plutonian's foster father Bill Hartigan. Although Bill genuinely loved and accepted Daniel like his own blood and wanted to instill good moral values and teach him to use his powers to help other people, his Misery Builds Character mentality, harsh teaching methods, and unyielding approach, as well as his failure to understand the severity of Daniel's emotional problems (thanks to him being bounced between multiple different foster homes and being subjected to All of the Other Reindeer) and what the boy really needed was love and support and to just be a normal kid rather than a hero in the making, all wound up making things much worse, adding a serious martyr complex and extreme sense of responsibility to the already long list of issues plaguing Daniel's psyche. Really, the whole world would have been a lot better off if Bill had let Daniel make his own decisions, even if it meant him never becoming a superhero.
In Volume 5 of Scott Pilgrim, Stephen Stills tells Knives that before Scott broke up with her, he had already started dating Ramona. Knives then tells Ramona, leading her to break up with Scott.
In the Sonic the Hedgehog (Archie Comics) book this applies to Sonic, Sally, Knuckles, and Tails's respective families. Issue 50 revealed that Sonic's dad and uncle found Robotnik and brought him to King Max, who made his infamous decision to make him the new Warlord. During this time up to when they were captured, Knuckles' father and ancestors were aware of Robotnik, but devoted none of their considerable resources to resolve those problems, despite Robotnik once trying to weaponize the Floating Island in the Sonic and Knuckles tie-in comic, trying to drive the island into the sea in the Death Egg saga and Knuckles spin off title revealing his family was still living on the island and would've been aware of this; Locke even commented on the Ultimate Annihilator in the spin off title. And almost immediately after they returned, Tails's parents caused a political reformation that may well have resulted in, in addition to King Naugus, the disaster Silver's trying to prevent.
Tusken-raised Jedi A'Sharad Hett was shown in Star Wars: Republic to have known Anakin Skywalker personally, and he learned of his genocide of his people but refused to report him believing that he needed to confront his inner darkness himself. After Anakin fell and became Darth Vader, Hett blamed himself for not intervening. Disillusioned, Hett returned to Tatooine and became a Tusken Raider warlord only to have his right arm severed by Obi-Wan Kenobi protecting Luke's homestead. Hett was exiled from Tatooine by Kenobi, who hoped he would see the error of his ways and return to the Light. He did the exact opposite and in Star Wars: Legacy went on to become a new Sith Emperor who created the One Sith, and started a new war that resulted in the deaths of billions.
Tales of the Jedi: A pair of hyperspace explorers, Gav and Jori Daragon, stumble upon the homeworld of the Sith race entirely by accident, trying to find a new space-lane to pay off their debts, just as the Sith are having a little leadership dispute. The Sith Lord Naga Sadow engineered a scheme where he frees the explorers, and lies to his people that the Republic will invade their empire, thus starting the Great Hyperspace War.
Before that, there's the Jedi themselves, some thousands of years before. During an argument with some of their own, the Jedi won, but rather than kill their defeated enemies decided to send them into exile, hoping they'd learn the error of their ways. The exiled Jedi wound up on Korriban, home of the Sith species... and the rest is history.
Inverted in the Tintin story The Secret of the Unicorn with the pickpocket who had been stealing everyone's wallets. He ended up stealing the Bird brothers' wallets which contained their parchments, this lead them to think that Tintin stole their wallets. They ended up kidnapping Tintin, and after a long chain of events, they got captured. Tintin got the last two parchments from the pickpocket and ended up finding Red Rackam's treasure.
In The Transformers (Marvel), Octopunch tried to shoot Grimlock during a battle in Cybertron's core. However, the blast harmlessly bounced off the Dinobot leader and instead struck Primus himself, causing him to let out a scream that allowed Unicron to find his way back to Cybertron.
In the IDW comics, Whirl is a minor example - while the Senate had pressed him into service, Megatron points to him as the one who taught him to rebel against the Senate with violence, thus starting the Great War.
Whirl: Did I ever tell you about how I started our war? You'll laugh your head off.
Early in the second season of Transformers: More than Meets the Eye Trailcutter and some other Autobots wind up stranded on an unknown world that was the site of a major battle. They find a mysterious Cybertronian who is dying of his wounds and in immediate need of an Energon transfusion. While the others are wary of the stranger, Trailcutter refuses to let someone die through inaction. Midway through the procedure it comes out that the stranger is not just a Decepticon, but Vos, the newest member of the Decepticon Justice Division who, along with his cohort Kaon, promptly murders Trailcutter and returns to his comrades. Vos's return helps pull the Decepticon Justice Division back together after a long period of post-War despondency and they become the primary antagonists of the season finale. Promotional cards for the second season call him "The Catalyst."
Speaking of the second season of More Than Meets The Eye, shortly after Trailcutter's death is the "Elegant Chaos" arc, which is arguably the biggest example in the entire Hasbro Comic Universe. In that arc, the crew of the Lost Light has to travel back in time to stop Brainstorm from seemingly assassinating Megatron. While they are successful, their actions do end up having some very dire consequences as the Functionist Universe (the timeline without Megatron) diverges from the main timeline and provides the setting and conflict for the third and final season. However, in the process of trying to stop Brainstorm, the crew of the Lost Light accidentally cause several Stable Time Loops, two of which are major cases of Create Your OwnGreater-Scope Villain.
While in Maccadam's Old Oil House, Tailgate asks for a curly straw, which ends up instigating a bar fight that leads to a young Megatron being arrested and subjected to Police Brutality at the hands of Past!Whirl. As mentioned above, it was that moment that led to Megatron losing his idealism and become more jaded and violent, an approach that would lead to the Great War that would consume Cybertron and the galaxy.
The most damning consequence of all was Present!Whirl (again?), Chromedome, and Rewind inadvertently tipping off the Senate on the activities of a certain senator. That senator would eventually be captured and sent off to the Institute to be brainwashed and mutilated, becoming the famously emotionless Decepticon scientist, Shockwave. It got even worse when "The Falling" arc of Optimus Prime revealed that "Onyx Prime" was in fact Shockwave, who had been sent back in time following the events of Dark Cybertron, and in the process of taking The Slow Path orchestrated much of Cybertronian history as part of an ontological paradox, including the war that led to the creation of the continuity's version of Unicron. Even though one might blame Whirl, Rewind, and Chromedome for accidentally triggering Shockwave's Start of Darkness, they would not have been there in the first place were it not for Brainstorm deciding to go back in time to fix everything. Congratulations, Brainstorm. You are indirectly responsible for triggering the greatest ontological time paradox in Transformers history.
, which ends up instigating a bar fight that leads to a young Megatron being arrested and subjected to Police Brutality at the hands of Past!Whirl. As mentioned above, it was that moment that led to Megatron losing his idealism and become more jaded and violent, an approach that would lead to the Great War that would consume Cybertron and the galaxy.