In The Adventures of Superman episode "The Perils of Superman", two crooks ask Perry how he'd describe the route to their hideaway. Perry describes the route, and the crooks use a recording of his voice to get Jimmy onto the roads in a car which they sabotaged.
Alex Rider: The video Tom makes when he finds out Alex has been recruited as a spy, which the Roscoe duplicate finds on Tom's phone after taking Tom prisoner and which blows Alex's cover at Point Blanc.
In The Americans, Stan spends much of season 3 working in secret with Oleg to prove that a supposed Soviet defector is actually a spy, all in the hopes that the FBI will capture the defector and trade her to the Soviets for Nina. It backfires; the FBI doesn't care about Nina, and instead trades the defector for a CIA asset who's being held by the Soviets. What's more, Stan's bosses are pissed that he ran an operation without their knowledge, and thus his punishment is that he has to keep working with Oleg.
The crew defeat the fallen power Jasmine, who took over the world through mind control and was eating people on a daily basis... and are later rewarded by the demonic law firm Wolfram and Hart for "Ending world peace" because during the short time Jasmine was in control, there was no war or fighting or hatred anywhere within her influence.
However, the Senior Partners actually intended to corrupt Angel and distract him from their planned apocalypse all along.
Also an example: waking Jasmine up in the first place by curing Cordelia's amnesia.
In "Not Fade Away", After Angel and his team assassinate all members of the Circle of Black Thorns, the evil forces of the world decide to pull out all the stops and unleash every available evil creature on LA.
What's worse is the demonic army is just the beginning. Wolfram and Hart's real reaction to Angel taking out the Circle is to send the whole of L.A. - every man, woman and child - to Hell.
Wesley: We set the captives free. Cordy: Well, actually, didn't we set a bunch of demons free? Wesley: Oh. Well. Technically, yes. Fortunately not all demons are evil, but we can't vouch for everyone they set free from the gladiator ring.
In season 3, Wesley's fooled by a fake prophecy that claims that Angel will murder his own son, and makes a deal with Angel's enemy Holtz to take him to safety, only for Holtz's second-in-command Justine to slit his throat and steal the baby herself, resulting in a sequence of events that led to Connor being trapped in the hell dimension Quor'toth, where he undergoes Training from Hell and emerges as an Ax-CrazyAntagonistic Offspring. Fake prophecy or not, Angel was understandably anything but pleased with Wesley.
Angelus summed it up best:
Angelus: Good old Wes. Always count on him to tackle a bad situation and make it worse.
In the first episode of Ash vs. Evil Dead, Ash gets high on marijuana with a woman and decides to read poetry to her, and said "poetry" was a passage from the Necronomicon. This leads to the Deadites attacking him again, setting the entire plot of the series in motion.
The Aquabats! Super Show!: At the start of "Cowboy Android!", a miner tells the Aquabats off for sealing a monster in the mine rather than getting rid of it, as this means they still can't work in the mine.
Are You Being Served?: In one episode, the group go on strike and become belligerent towards management following over-the-top supervision of coffee and bathroom breaks. The result is a compromise imposed by Old Mr. Grace that effectively eliminates the coffee break altogether.
Barry opened a time portal to save his mother, resulting in a tear between universes, allowing Zoom to terrorize Earth-1.
Barry went back in time to save his parents, resulting in an altered universe complete with an evil version of himself hell-bent on destroying everything Barry loves. This also resulted in undoing Eobard Thawne's erasure from existence, which led to another group of heroes breaking it (see below).
Guys, we really want Barry back. So let's pull him out of the Speed Force. Yay! He's back! Oh, shit, we just created a dozen new dangerous metas. To be fair, though, this particular chain of events was manipulated by the Thinker.
During a fight in 1975, a piece of Ray's Atom suit is broken off. Finding it, Vandal Savage reverse engineers the advanced technology and takes over the world 200 years before schedule.
Rip chews out Mick's stupidity and reveals that he only brought Mick along as a "package deal" with Snart. Realizing he's not wanted, Mick joins a gang of time pirates to try and take over the ship.
Snart strands Mick in a remote past, intending to come back for him. But to Mick, years pass and he's near madness when found by the Time Masters, who turn him into the deadly Cronos to hunt the team.
The team try to convince a young Per Degaton to go off the path that will turn him into a tyrant. Instead, they not only push him toward it but accelerate Savage's own rise to power.
Joining with the team in a trip to the 1950s, Cisco Ramon saves a captured Dominator from government custody. In the present, Cisco discovers that the same Dominator saw him use powers, realized the threat mankind could be and prepared this invasion.
In 1927, Ray lets Eliot Ness go with a couple of men he thinks are cops to lead him to the courthouse. The result: Al Capone becomes mayor of Chicago in a few years.
The team try to save Rip Hunter, who's a filmmaker in 1967. The fight causes Rip's assistant George Lucas to quit filmmaking entirely and be an accountant. Thus, he never makes a certain pair of iconic sci-fi properties which never inspire both Ray and Nate to follow their scientific/scholar pasts and the duo slowly turn into idiots.
Facing what he thinks is a hallucination, Mick lets a time-lost Snart know about the team's plan to capture the Spear of Destiny.
After the team give him grief over his stupidity, Mick decides to join the Legion of Doom and steal the Spear.
Nate accidentally lets Julius Caesar know about the Ides of March. After taking out Anthony and Brutus first, Caesar creates a Roman Empire that lasts into the 21st century.
In the episode "Compromised", their mission to investigate a time anomaly in the White House during the Cold War goes south when Sara discovers Damian Darhk, the man who will one day murder her sister, is around and immediatly tries to murder him, leading to a fight between the team and White House secruity. She does again later in the same episode, giving Damian a Breaking Speech that informs him of his own future, where he ends up defeated and killed by the Green Arrow, causing him to ally with evil time traveller Eobard Thawne/Reverse Flash, creating a much bigger threat to the timeline. This trope is taken Up to Eleven in the Season 2 finale, when the Legends crash-land in LA of 2017... filled with dinosaurs and buildings from different time periods.
Sara Lance: Guys? I think we broke time.
It's no wonder that Rip finally says "enough" and forms the Time Bureau, a new organization dedicated to keeping history straight, and benches the Legends. Then he allows them to time travel again, fixing small problems (some of which nearly turn into huge problems because of their incompetence). Then they try to investigate a possible vampire attack in Victorian London, resulting in Damien Darhk being brought back to life, more powerful than ever. Though it should be noted that most of that is actually Rip's fault. It even results in him being fired from the Time Bureau.
Referenced in the Elseworlds (2018) crossover. When Oliver wakes up and everyone thinks he's Barry, he immediately assumes it's Barry's fault. For once, it wasn't, but even Barry's own team can't help but jump to that conclusion.
Iris:[to Oliver] Barry, did you travel through time again? Barry: No, I swear I didn't.
Atomic Train: In this TV movie, a train driver following behind a runaway train in an attempt to rescue the occupants, ignores orders to pull back, muting his radio in the process. With the radio muted, he is unable to hear the fact that the runaway has managed to stop. This results in him ramming into the rear of it, causing it to run away again.
Nice job taking the tougher, advanced battlestar capable of building Vipers and ramming it into a Cylon Basestar to save the aged, more obsolete battlestar, Lee. Especially since the Galactica is now falling to bits entirely.
Nice job creating an army's worth of Cavils and their war machine and letting them box you, Saul, Ellen, Sam, Galen, and Tory.
Nice job killing Tory on the spot and losing any chance of peace with the enemy Cylons, Galen.
How about what lead to the fall of the Twelve Colonies and the near-extinction of the human race? Nice job thinking with your dick and giving the mysterious woman you barely know, access to the Colonial defence systems in exchange for sex, Baltar!
FBI Agent Seely Booth allowed a man convicted of killing a teenage girl (and was less than 30 hours away from being executed for the crime) convince him to reinvestigate the case by providing crocodile tears in prison. He did eventually learn that he was right about the man being the killer all along, but said investigation turned up even more bodies, which prevented the man from being executed before the investigations could be completed (which would likely take years). Even worse, the killer eventually escaped from prison and killed another woman and ended up stalking his potential love interest, Dr. Temperance Brennan. Seriously, nice job breaking it, hero.
In another episode, Booth comforted a woman who had been stalking that week's victim, causing her to become obsessed with him. This led to the woman trying to kill Bones out of jealousy, Booth getting shot while protecting Bones, and Bones shooting and killing the woman when she tried to shoot her again.
The Boys (2019): Homelander dooms Flight 37 by frying the controls with a careless use of heat vision. Had he not, even with the pilot dead there would have been multiple options to save it.
In "Live Free or Die", Walt and Jesse formulate a plan with Mike to use a powerful supermagnet to destroy a laptop belonging to Gus that has incriminating security footage of the three working for Gus's drug empire. The plan works, but in the ensuing chaos, they break a photo frame, revealing papers containing offshore bank accounts of people Gus paid to silence people involved in his business, plus an account set aside for Mike's granddaughter, which the DEA immediately seizes. Adding insult to injury is the fact that Gus saw fit to keep his laptop heavily encrypted, so the DEA couldn't find out what was on it anyway.
Walter White's storyline is a series of unintended consequences. All of his solutions create bigger problems, particularly when his plan to exact revenge on Jack and his crew for stealing his money and murdering Hank literally ricochets back at him.
When Walter indirectly kills Gus Fring in order to protect his family, he ended up ruining the company and prevented him from earning further money. As a result, Mike, Gus's devoted bodyguard, lampshades this during his brutal rant.
Walt: I want those names, Mike. You owe me that much. Mike: I don't owe you a damn thing. All of this, falling apart like this, is on you! Walt: Wow. (disbelieving chuckle)Wow! Oh, that's some kind of logic right there, Mike. You screw up, get yourself followed by the DEA, and now suddenly this is all my fault? Why don't you walk me through this, Mike? Mike: We had a good thing, you stupid son of a bitch! We had Fring, we had a lab, we had everything we needed, and it all ran like clockwork! You could have shut your mouth, cooked, and made as much money as you ever needed! It was perfect! But no! You just had to blow it up! You, and your pride and your ego! You just had to be the man! If youd done your job and known your place, wed all be fine right now!
In "Consequences", when Faith begins to go bad after staking the Deputy Mayor, Buffy and Giles plan to deal with it without alerting the Watcher's Council, but Wesley finds out anyway after eavesdropping on them and immediately calls in a special ops team to bring her in. In the process of doing so, he completely ruins Angel's attempts to get through to her just as he was beginning to succeed, setting off a sequence of events that lead to Faith becoming Mayor Wilkins' dragon.
Giles:(flipping pages) I have it, I have it. Uhm, "The summoning spell for Gachnar can be shut down in one of two ways. Destroying the mark of Gachnar..." (Buffy walks over to the mark and puts her fist through it, ripping up the floorboards. Gets up and looks over at Giles with a proud smile) "...is not one of them and will in fact immediately bring forth the fear demon itself."
Good thing the fear demon itself is only four inches tall.
Buffy does Angel, which causes him to lose his soul and revert to his evil mind rapist self. Nice job having the hots for a vampire, slayer. Of course, Angel gets equal blame for not keeping it in his pants despite knowing full well his curse. Though in his defense it's not like he knew that there was a way to break it. Speaking of which, when the gypsy tribe cursed Angel in the first place, it was actually a pretty dumb idea of them to allow a way to break Angelus back as their idea of making Angel suffer more. Especially since that part bit them in the ass when he did.
Played straight - somewhat - with the demon Balthazar in Season Three. Balthazar was Mayor Wilkins' rival - had he regained his power, he would have killed the Mayor. By killing Balthazar, Buffy eliminated one of the two major threats to the Mayor. Of course, the other major threat was herself...
And, of course, when Buffy was brought back from the dead, thereby ripping her out of heaven. From Buffy's point of view, at least, nice job breaking me, Scoobies.
Then in Season Eight Buffy needed funds, stole from a bank... which resulted in a rogue Slayer and a very unhappy military. Giles sent Faith undercover to assassinate a dangerous Slayer. Buffy misunderstood. Faith didn't react well. Willow's flaying of Warren comes back to haunt her. And everyone else. That was just the beginning.Nice job- oh never mind.
Buffy created the Twilight dimension by screwing Angel, which let thousands of demons invade Earth, which resulted in the destruction of the Seed of Wonder and removed all magic from the world.
While we're at it, nice work imitating Twilight, becoming possessed and killing Giles, Angel.
Buffy destroying the seed in Season 8. Willow blames Angel.
Nice job turning your back on Management in one finale and shooting Strickler in another, Michael. You now have even less of a clue about what's going on, and you almost got yourself into even hotter water.
This seems to be a running theme for each season cliffhanger, but most notably when Michael finally seemed to have beaten those responsible for his burn notice, only to find out that his efforts unearthed the man in charge of the entire conspiracy that resulted in Michael's burn notice and who forced Michael to work for him under the threat of having Fiona locked away.
Charité at War: Soldier Paul Lohmann, returning from war with a crippled leg, is under suspicion of having caused the injury himself and is threatened with being charged for "undermining the military force" by the Nazi regime. Co-veteran Otto lies for him, but his story doesn't match Lohmann's own report of how he got his wound; as such, Otto almost gets himself in trouble and gives further reason to doubt Lohmann's honesty.
Charmed: The episode "Coyote Piper" revolves around a spirit escaping from her demonic scientist creator. She eventually possesses Piper, and uses Piper's body to get her sisters to kill the demonic scientist when he comes to look for his creation... making it significantly harder to deal with the spirit. The demon's final words "You fools! She will destroy you!", are somewhat apt.
Combat!: In about 8:23 of this clip from this 60s-era World War II series. One of the characters says "Nice going, hero" after another is forced to shoot a German sentry they were supposed to take alive, not only depriving the unit of a prisoner to interrogate but also attracting the unwanted attention of even more enemy troops.
Dear White People: Corresponding with the above N-Word Privileges, Gabe was the one to call on Campus Security in order to break up the ensuing fight. Gabe didn't predict that one of the security guards would pull a gun on Reggie.
"The Romans": The Doctor accidentally gives Nero the idea to burn Rome. And has a Squee! reaction.
"The Ark" contains two major ones in the same story. The Doctor arrives on board a generation ship, unwittingly exposing everyone within to the common cold. This turns into a plague due to their lack of resistance and many people die until the Doctor can engineer a cure. This would be bad enough if a TARDIS glitch didn't cause him to accidentally travel hundreds of years further in time to the future, revealing that the plague had created conditions for the humans' slave race to rebel and enslave the humans.
"The Web of Fear" ends with the Doctor having manipulated the Great Intelligence into plugging him into a machine that drains his knowledge and memories into the Intelligence, but has secretly "crossed the wires" so, when the machine is switched on, the Great Intelligence will drain into him. The Doctor fails to explain to Jamie what he's planning beyond hinting it heavily, but Jamie can't figure the plan out, decides enough is enough and attacks the Intelligence. The result of this is that the Intelligence lives, but is rendered unable to continue flooding London with Yeti, if nothing else.
"Genesis of the Daleks", a story in which the Fourth Doctor is given the opportunity to prevent the creation of the Daleks by touching two wires together, opened multiple cans of worms in this regard:
Not only does he refuse, he keeps his companion Harry from doing it. Reason? What about all the good that might have been accomplished because the Daleks exist? Dare he destroy an entire race, even an evil one? Of course, years later he does just that, only now, because he waited, he's annihilating two species, the Daleks and his own. And that to stop a war that he himself could have prevented.
One Eleventh Doctor comic suggests that not only was the Fourth Doctor's refusal to kill the Daleks the cause of the eventual genocide he created, but actually "the first shot" in the Time War, which caused the Daleks to retaliate against the Time Lords and lead them into the war that resulted in their double genocide by the Doctor in the first place.
Bonus points for the Time War. The Doctor "ended it" by killing off the Daleks and the Time Lords, right? Wrong! Some Daleks have escaped and are regular villains in the new series. The Doctor has been good at keeping the Time Lords dead, though. Nice job, Doctor. (Well, until the 50th anniversary special.)
"The Face of Evil" reveals the long-term implications of some ill-advised world-saving the Fourth Doctor did while still experiencing post-regenerative trauma and having a minimal idea of who he was and what was going on. He ditched UNIT to travel in the TARDIS, rebooted a computer by giving it his own personality, and all this did was drive it mad and cause it to become an evil computer "god" with his own face. On the bright side, this also "created" his future companion and friend Leela, a woman from the civilisation created by the mad computer.
In the TV Movie, the Doctor is rushed to hospital after being shot, where the cardiologist on duty, Grace, begins to operate on him, despite the Doctor repeatedly trying to get her to stop due to his Bizarre Alien Biology (finally being silenced by being pumped full of anesthetics). During the operation Grace gets lost and freaks out due to the Doctor's different biology, a medical probe breaks off inside the Doctor, and he has a seizure and dies. It gets worse however, as when his regeneration finally kicks in it's botched up due to the ton of anasthetics, and the Doctor ends up wandering around the hospital confused and with amnesia. All this could have been avoided if Grace simply hadn't operated on the Doctor.
"The Long Game" ends with the Doctor thinking he's saving the world by shutting down a space station that controls an Earth-spanning propaganda regime. In "Bad Wolf", however, he returns to Satellite 5, a century later and learns that as a result of the shutdown, Earth has become technologically and socially stagnant, and the station itself has become a clearinghouse for lethal reality shows secretly run by the Daleks.
"Father's Day": Rose saves her father from the car that's supposed to kill him despite the Doctor warning her not to do more than SEE him physically. Cue the Reapers appearing and starting to devour everyone in sight just to heal the wound she's created. It gets worse, though. When the Doctor finds a solution that will bring everyone back and keep her father alive, he warns her not to touch her past self. Rose, of course, does this (well, her past self was thrust into her arms), ruining the Doctor's solution and getting him consumed in the process. As a result, the only way to stabilise time is for Pete Tyler to sacrifice himself ... Rare case of the hero breaking it twice in one episode.
"The Empty Child"/"The Doctor Dances": Captain Jack Harkness spends most of the story being rather flippant about the situation involving people turning into gas-mask zombies. When the Doctor deduces that the spaceship Jack carelessly sent crashing to Earth as part of a con he was attempting to pull on the Doctor and Rose (who he had assumed were Time Agents) is the source of the nanogenes responsible, he makes a point of explaining to Jack in very precise terms just how he's doomed the entire human race, while glaring at him. Jack is a lot less flippant afterwards.
It's been suggested (including in a column by Russell Davies) that the Doctor's self-righteous overthrowing of Prime Minister Harriet Jones after her actions in "The Christmas Invasion" directly allowed the Master to take her place, conquer the world, and rule in an unequalled reign of terror and genocide for an entire year until things managed to get sorted out. By contrast Harriet's truncated term, according to the Doctor himself, would have been "a Golden Age". Nice going, Doc. Originally, this was going to pointed out by the Master in "The Sound of Drums"/"Last of the Time Lords". However, it was decided that this sort of gloating in addition to the abuse the Master had already heaped upon the Doctor would be an overkill.
It also allowed the Prime Minister seen in Torchwood: Children of Earth to come to power. Perhaps Harriet Jones would have had stricter morals about dealing with the 456. Which also means the Doctor is responsible for causing even more pain and suffering to a friend, since it's the lack of government action that leads Ianto to die with Jack confronting the 456, and Jack to sacrifice Steven.
"Tooth and Claw": The Tenth Doctor and Rose save Queen Victoria from a werewolf, but because they act like selfish, immature adrenaline junkies, she decides to found the Torchwood Institute to protect the British Empire against extraterrestrial threats. They then spend a good century robbing and murdering innocent alien passers-by, and nearly destroying the human race several times For Science!
"Doomsday": In a subversion, Mickey accidentally touches the Daleks' Genesis Ark during a Dalek/Cyberman/human scuffle. However, the Doctor thanks him, as otherwise the Daleks would have tried to open it by force, with massive levels of collateral damage as in, trying to switch off the Sun kind of collateral damage.
"Human Nature"/"The Family of Blood": The Doctor masquerades as a human in 1913 rural England to evade four aliens who want to steal his longevity. Assuming they don't find him, they die of old age in a few months, right? Wrong! Of course, they do find him, and go on a rampage, killing many innocents. In the end, the Doctor re-emerges and saves the day. Victory, right? Wrong! Love interest Joan, grief-stricken at the "death" of the Doctor's manufactured human self, points out that all the death and suffering was the result of the Doctor coming in the first place. By trying to be kind to the bad guys, he ended up being cruel to the innocent bystanders. Even the Doctor seems to accept that this is true.
"Utopia": Martha Jones inadvertently manages to intrigue Professor Yana enough to have the Perception Filter on his Chameleon Arch pocket watch fail, leading him to open it and turning him back into the Master.
"The Doctor's Daughter": The Doctor inadvertently reveals more of the map of the base, resulting in both sides of the ongoing conflict preparing to go to war over the newly-discovered "temple".
"The Waters of Mars": At the end, it's heavily implied that the Doctor broke Time itself. Or, rather, he would have if Adelaide had not made the ultimate sacrifice to set things straight.
"Victory of the Daleks": The Doctor's attempt to force the Daleks to admit their true intentions culminates in him screaming "I AM THE DOCTOR, AND YOU ARE THE DALEKS!" Unfortunately, this "testimony" causes the Daleks' Progenitor device to accept that they are the Daleks (it didn't recognise them as they weren't "pure"). At this point they reveal their true identity, start killing people and make more Daleks which proceed to turn on all the lights in London during the Blitz, make an earnest attempt at blowing up the Earth and then escape to their own time period to recover and rebuild. Nice job endangering the entire universe throughout the whole of history, Doctor.
"Cold Blood": Ambrose giving in to her distress over what was happening to her various family members and letting herself be goaded into killing Alaya gives General Ripper Restac all the excuse she needs to declare war. In the process of trying to stop this, Rory is eventually killed and retgoned.
Eleven runs into this again during "A Christmas Carol". He resorts to going back in time and rewriting the entire childhood of Kazran, the only man who can save a spaceship from crashing, only for Kazran to end up exactly as bitter and jaded as he was already, just for different reasons. Then, when Kazran finally does agree to help, the all-important machine no longer recognises him as the man it's programmed to obey. And of course, the Doctor's rewrite involved an act of kindness that kind of backfired: he let Abigail out of her cryogenic prison every Christmas, not realizing that every day she left was one day closer to her death up until she had one day of life left. When Kazran realized this, it brought about the bitterness mentioned above.
"A Good Man Goes to War": The Doctor's name inspires such fear that he can end conflicts without fighting and no loss of life, which is what he always wanted. Unfortunately, the enemies were so fearful of the Doctor that they stole Amy and Rory's newborn daughter, Melody and raised her as a weapon to kill him. The Doctor doesn't realize he created this until River Song (who is Melody Pond as an adult) calls him out and points out this was his doing:
River Song: I couldn't have prevented this. The Doctor: You could have tried! River Song: And so, my love, could you. The Doctor: You think I wanted this? I didn't create this! This... this isn't me.
"Let's Kill Hitler": Hitler thanks the Doctor for saving his life. (Technically, this was Mels'/River Song's/Melody Pond's fault since she threatened the Doctor at gunpoint, shot the TARDIS and caused it to crash at the wrong time.) Doesn't stop the Doctor from saying this (although, since it was 1938, Hitler isn't scheduled to die for another 7 years):
The Doctor: Believe me... it was an accident.
"The Wedding of River Song": In an attempt to save the Doctor's life, River Song tries to overcome her programming to shoot the Doctor by wasting all her shots, breaking what should be a fixed point in time. As such, all of causality breaks down, and all of existence on Earth happens at once. The Doctor berates her for her willingness to hurt all of reality for him, but in an odd turn for a hero, she doesn't care. In the end, it turns out the Doctor had his own plan for getting out of it, so she really need not have bothered.
"In the Forest of the Night": This nearly happens with the government engaging in deforestation. The Doctor is able to stop this by sending a message across the world.
A key thread of the Series 9 Story Arc involves this trope. In "The Girl Who Died" (which starts with mounting examples of this trope Clara tries to help a Viking villager and they end up teleported onto an alien ship as a result; said villager then provokes aliens who already had what they wanted into fighting), in the wake of tragedy the anguished Doctor rashly decides to save sweet, innocent Ashildr from death; problem is, the only way he can do it turns her immortal. He almost immediately worries he's invoked this trope, and he's eventually proven right, in that Ashildr is near-sociopathic a few centuries later and resenting him for "trapping" her in life. While he tries to make up for the damage he's done and helps stop further disaster in "The Woman Who Lived", it's not enough, in that in "Face the Raven", she betrays him to the Time Lords in 2015 in exchange for protection of a "trap street" an act that inadvertently leads to the death of Clara and he undergoes torture. The end result of these mounting miseries is that the Doctor temporarily turns into a Woobie, Destroyer of Worlds and almost destroys the universe before being brought back to his best self.
"Resolution": Insofar as the UK government is on the side of the protagonists, its decision to suspend UNIT operations due to budgetary concerns leaves the entire Earth in danger, even besides the in-episode consequences of the regular military and police who encounter the villain being completely out of their depth and getting slaughtered.
"Orphan 55": The Doctor's insistence on attempting to rescue Benni after he is captured by the Dregs leads directly to the deaths of at least three people.
Eternal Law: In one episode, the angels' case of the week is preventing a woman from committing suicide. By the end of the episode she seems to have found some sort of peace, despite going to jail for murdering her son's killer... and then Tom reveals himself as an angel and promises she'll be reunited with her son in heaven. She promptly commits suicide to get to the afterlife straight away.
In virtually every episode, when Urkel comes in contact with something, usually one of Carl's prized possessions, usually followed by Urkel uttering one of his catchphrases, "Did I do that?"
In one case, "nice job breaking it" set up an entire plot where Urkel was unusually angry at Carl and declined to explain; he kept swatting Carl on the head with a newspaper. It turned out an Urkel in shining armor had broken Carl's prized model ship-in-a-bottle that had been left prone on the kitchen table, thanks to the nerd's awkward handling of a lance. Carl — unwilling to see the whole thing was his own fault due to leaving the model ship where it could get broken — was very angry and threw the nerd out of the house, before fuming aloud that he'd wish Urkel would just go away forever (Urkel had accidentally overheard Carl rant about his broken ship). Carl eventually realizes his words were inappropriate and apologizes.
This however can be considered a Broken Aesop due to the number of times Steve as pulled the Wounded Gazelle Gambit. Laura eventually called him out on the fact that every time she gets fed up with his antics he guilt trips her into forgiving him.
Farscape: Nurse Kelsa from the episode Different Destinations. Without assessing the current situation using either her own eyes or trying to seek and explanation from Crichton, she decides to put an arrow though the chest of an imprisoned enemy General that was about one hour away from brokering a peace deal that would have protected the women and children from slaughter. The results? she is not only technically responsible for the deaths of everyone present (including the one man that survived in the original timeline) but was also responsible for nearly destroying the future of that entire part of space. The best bit however comes later in the episode when she still refuses to believe Crichton was innocent of treason and threatens to shoot Aeryn when she tries to untie him even though she was standing right there when another enemy official confirmed everything Crichton had claimed and basically pointed out that she was responsible for dooming them all. To give her credit though; she is saved from Too Dumb to Live status by the fact it was the main cast travelling back in time that put her in that situation in the first place - breaking it long before it was her turn to.
FlashForward: During the Mosaic team's trip to Somalia, their resident morally-ambiguous CIA agent Vogel kills the one man who was destined to bring peace to the war-torn nation. He doesn't seem to care too much.
The episode "The Preachification of Convincing John": Mokey decides that eating the constructions Doozers work so hard to build hurts their feelings. Without bothering to ask the Doozers themselves how they feel about the situation, she enlists the help of Convincing John to convince all of Fraggle Rock that eating Doozer constructions is wrong and binds them in the nigh-unbreakable Solemn Fraggle Oath never to do so again. So the Doozers build and build with no one to eat the constructions — and end up crowding both themselves and the Fraggles nearly out of house and home. Eventually, Mokey overhears Doozers lamenting about having to move out of Fraggle Rock. She realizes she had them all wrong. They like the Fraggles crashing in since it means they can keep on building, and she quickly undoes the Oath.
Congratulations, Sansa! Lying to the king and queen about Joffrey got your own direwolf killed!
Congratulations, Ned! Ignoring Littlefinger and Renly's advice and showing mercy to Cersei's illegitmate children by warning Cersei you know about them has led to Cersei and Joffrey ruling, your guards all being killed, Robert's death, which is the very reason you became Hand in the first place, you being arrested and eventually killed, the death of several of your family members and the destruction of your entire House! Varys called him out on this the following episode, pointing some of this out.
Capturing Tyrion Lannister has compromised the safety of your husband and daughters in the capital, caused his really pissed off father to unleash Gregor Clegane on the lands of your own family and helped spark off a civil war between your family and the Lannisters! Whilst Gregor Clegane pillages your father's lands, Jaime Lannister starts a fight with your husband in the streets! Your only evidence was Littlefinger's testimony and even then, Ned insisted on a measured approach while you arrested Tyrion on the spur of the moment and then kidnapped him by taking him to the Eyrie.
Releasing Jaime Lannister has undermined your son's authority, making him look weak and unable to control his own people, enraged his bannermen and deprived your side of an extremely valuable hostage with nothing in return. Also, there was absolutely no guarantee that the Lannisters would agree to release Sansa and Arya even if they got Jaime back.
The death of Rhaegar Targaryen at your hands. Rhaegar was a perfectly sane, popular, and highly charismatic man, who many in Westeros looked forward to eventually taking the throne, especially because it would rid them of his utterly despised father Aerys's nightmarish reign. Instead, you took the throne for yourself in conquest and in less than 20 years, managed to bankrupt the entire realm and sow the seeds that would lead to the outbreak of civil war and a foreign invasion after your death. Then again, the Mad King himself was shaping up to be one of the better Targaryen kings before he rather suddenly went insane, so we can't be sure Rhaegar's future didn't hold similar insanity.
Sending assassins after Daenerys managed to piss off Drogo enough that he changed his mind about not invading Westeros!
Saving a wise woman from rape and then asking her to save the life of your husband has led to said husband winding up as an Empty Shell and your son to be stillborn.
Despite liberating the slaves in Astapor and Yunkai, those two cities end up back in the hands of despots as soon as you move along. In Meereen, your negligent care of her dragons has caused collateral damage. Furthermore, your Black-and-White Morality approach to punishing the Masters has resulted in the deaths of some of the more sympathetic political figures as well. Leaving your dragons unattended leads to the death of a three year old girl.
Good job, Mirri! Destroying everything of value to the naive queen you sought revenge against has made her more cunning and dangerous than her deceased husband or stillborn son could ever have been. Bonus points for teaching her that mercy is for the weak, giving her a crash course in blood magic, and providing the means for her to hatch three dragons.
Sending Theon home in an attempt to gain military support resulted in the exact thing your father prevented by keeping Theon as a hostage in the first place, and now you have to fight a war on two fronts!
Breaking a sacred vow that you will marry the daughter of an important ally (who allowed your army to cross his territory in addition to providing you with several thousand troops) will likely get you tagged as an oathbreaker, not to mention harming your military position and giving the notoriously prickly and treacherous head of the family a good excuse to betray you. These actions come back to haunt Jon and Sansa three seasons later, as they blame Robb for dragging their family members into war and getting them killed.
Executing Lord Karstark despite all counsel lost you the support of his soldiers, forcing you to turn to the infamously untrustworthy Freys whom you already pissed off by breaking a marriage pact!
By inciting Renly to make a bid for the throne you made a civil war worse and got your lover killed.
By telling Olyvar about your secret betrothal, the information is passed to the Lannisters, who move to block your family's plan.
In his youth, Jaime engineered a Rescue Sex scenario in the benefit of Tyrion. His younger brother, unaccustomed to kindness, fell in love and married the girl, who was actually a sex worker. Tywin put an end to it; he pimped her out to his whole guard and forced Tyrion to watch, leaving him mentally scarred for life.
Jaime lies about Brienne's family wealth to prevent Locke from raping her, but later, on his way back to King's Landing, he hears that Locke refuses her father's ransom offer because he expects more and finds a mere 300 gold dragons an insult coming from an island full of sapphires. (In fairness, Jaime then turns right around and rescues her.)
The Stark's dislike for Lannisters leads them to buy Littlefinger's lies about them killing Jon Arryn, actions which helped spark the War of the Five Kings.
Arya Stark has a few:
Hitting Joffrey and running away with Nymeria, leading directly to Mycah and Lady's death.
Her attempt to steal a letter from Tywin is discovered by Amory Lorch, who is in turn killed by Jaqen right in front of Tywin's eyes. Tywin believes then that the assassination was meant for him, and he responds by ordering all the farms and villages around Harrenhal to be ravaged and his own men to be decimated as punishment. Later Arya realises she should have gotten Jaqen to kill Tywin, the Dragon-in-Chief of House Lannister, right from the start. And why not Joffrey and Cersei while she was at it, as Gendry later points out.
Arya's Hot-Blooded personality finally takes a direct toll on her in "The Bear and the Maiden Fair", when she irrationally runs away from the Brotherhood, in a war zone, with no supplies and in the middle of the night, only to find herself made a prisoner by The Hound immediately.
In Season 6, when she decides to abandon the Faceless men, she's stabbed several times for her troubles and manages to get help from a woman she previously saved...which then leads to Lady Crane getting brutally murdered by the Waif.
Bran is ultimately responsible for making Hodor the way he is. In the same episode, Bran's actions inadvertently cause the deaths of the Three Eyed Raven, Summer, several Children of the Forest, and Hodor.
Also, his order to Rickon and Osha to seek refuge with the Umbers ultimately results in them being betrayed and turned over to Ramsay, with both dead by the end of the season.
If the sacrifices to the Lord of Light are actually useful, Davos' decision to save Gendry from Melisandre indirectly leads to another sacrifice of royal blood - and this time Shireen is the one who is sacrificed.
In Brienne's attempt to protect Arya Stark, she ends up (supposedly) killing Sandor Clegane, the only person left that was keeping Arya safe. And to top things off, she loses track of Arya.
The Children of the Forest, it's revealed in season 6, created the White Walkers as an army to drive humanity away from their land. In an added irony, the White Walkers ended up turning on their creators as well, turning the lands beyond the Wall into a frozen wasteland in which they hunted their creators down, due to being cut off from the human territories beyond. With the season 6 finale, it's implied that the Children of the Forest have now been wiped out entirely by their creations, in a truly ironic death.
Jon and Daenerys as of the end of Season 7. Jon & Friends go north of the Wall to attempt to capture a Wight to bring back to prove the threat to Cersei. While out there, they get surrounded by White Walkers and their army and trapped on an island in a frozen lake. They manage to get word to Daenerys, who arrives with her three dragons to help. During the fight, the Night's King stabs Viserion with a magical ice-lance, causing him to crash into the frozen lake and die. After Daenerys and the others get away, the Night's King has his army pull Viserion's body out of the lake, and raises him as an undead dragon. He then rides undead Viserion and uses him to attack the Wall with his fire breath. Viserion's attack causes the wall to shatter, leaving a gaping hole in it, which allows the army of the Dead unhindered access to the Seven Kingdoms.
Rhaegar Targaryen's love affair and elopement with Lyanna Stark ultimately led to the end of the Targaryen dynasty. His defeat at the Trident drove Tywin to turn on Aerys and sack King's Landing, which led to the deaths of his father, his children, the rape and murder of Elia, and the exile of his mother, brother, and unborn sister.
In "Histories and Lore: Dragons", Maester Pycelle states that in King Aegon V Targaryen's final years, he became obsessed with dragons and burnt himself and several others in an attempt to hatch dragons at Summerhall. Bear in mind this is Maester Pycelle we are talking about, but the Summerhall disaster is mentioned numerous times in the Lore. In the books, he wasn't "obsessed" with dragons the way that his crazy older brother Aerion Brightflame was. Rather, from all the time he spent wandering Westeros with Ser Duncan, he became a populist reformer after he was crowned, raising taxes on the rich lords to ease the suffering of the peasants. This made him a lot of political enemies and the great lords of the realm started to oppose him at every turn. As the years went on and such frustrations mounted, he became honestly convinced that having a couple of dragons like Aegon the First did was the key to keeping all of the great lords in line and pushing through his reforms. He had nothing but good intentions, but they ended up killing him, his best friend, and his eldest son in the fire.
Season 7 can be summarized as "Tyrion Lannister Ruins Everything". Let's list his failures in order:
Proposes a military strategy that results in all of Daenerys's Westerosi allies being killed or captured.
Allows Cersei to play him in order to convince the heroes that she will join them against the White Walkers, giving her the chance to retake the continent.
Convinces Jon and Daenerys to send an expedition north to capture a wight. After it predictably goes horribly wrong, he then fails to dissuade Daenerys from bailing out their allies. This allows the Night King to gain access to an undead dragon. In short, Tyrion broke the wall for a scheme that was doomed from the start.
The assassination attempt on Daenerys that he orchestrated was bungled, and Khal Drogo EXTREMELY pissed off, pushing him to start preparing an invasion of the Seven Kingdoms. This was almost certainly his planned result however, being part of the conspiracy backing the invasion.
An even more obvious one is him warning Olenna Tyrell about Littlefinger's ambition and trying to set up a marriage between Sansa and Loras. In retrospect, he just gave Olenna a glowing recommendation of the one man other than them, who was ruthless enough to pull off a regicide and serve as her partner-in-crime. This led to Joffrey's assassination, so not a great loss all in all.
Mossador takes it upon himself to slaughter one of the Sons of the Harpy after Daenerys resolves to give him a fair trail, and claims to have done so as a favor to her, clearly expecting to be praised for his efforts. This forces Daenerys into a Sadistic Choice between either abusing her power, or making a deep political and personal sacrifice. The end result; Daenerys loses a huge chunk of her loyal supporters, a massive riot breaks out, and Mossador loses his head.
Stannis's decision to assassinate Renly causes the Tyrells to join the Lannisters, which leads to his defeat at the Battle of Blackwater. Of course, if he hadn't assassinated Renly, they would have killed him within a day.
In a roundabout way, Olenna's assassination of Joffrey ultimately leads to the downfall of her house. Had the assassination not occurred as it did, Tyrion would not have taken the blame and Tywin would not have sentenced him to death. Had Tywin not sentenced Tyrion to death (cruelly using Tyrion's lover as a witness against him in the process) Tyrion would not have murdered him during his escape. Tywin's death left a power vacuum in King's Landing and precipitated the rise of the Sparrows, who imprisoned Loras and Margaery and ultimately got them killed in Cersei's destruction of the Sept of Baelor.
Get Smart: Max regularly did this - while he usually beat KAOS, he often destroyed the secret prototype or got the informant killed in the process. While Max was the main offender, however, even 99 and the Chief managed this on occasion.
Ghostwatch: The parapsychologist Dr. Pascoe in this infamous BBC special wants to use the program to justify the family living in the haunted house and bring their suffering to public attention. By doing this, she ends up creating a massive, nationwide séance that amplifies the ghost's power across the entire country.
In the season 2 premiere episode, Rachel's Attention Whore tendencies cause a new girl who is an awesome singer to join Vocal Adrenaline after she sends her to a crack house to keep her from stealing her spotlight. Though the only reason that the girl joined Vocal Adrenaline was because Sue made a call to the new VA coach because Will wouldn't help her antagonize the new football coach anymore.
Admittedly, almost all of the glee club's problems are caused by the stupidity/selfishness of Will or one of the glee kids (usually Rachel or Finn). This happens pretty much Once per Episode just so everyone can learn An Aesop at the end.
Dorothy on The Golden Girls had an immigrant student who wrote an essay on the experience of immigration which she thought was deserving of an award. She submits it to a literary company and it gets him an honor. Unfortunately, it also attracts the attention of the INS. It turns out he was an illegal immigrant and despite Dorothy's best efforts to keep him in America, he gets deported.
Gotham: Nice job not killing Oswald Cobblepot like you were supposed to, Jim Gordon. Now he's murdered countless others and started a gang war that left him the sole mob boss in Gotham City.
On Growing Pains, Michael discovers that the school is going to fire Coach Lubbock due to budget cuts. After failing at every legal move to prevent this, Mike organizes a sit-in. This results in the protesters all getting arrested and the school fires Coach Lubbock immediately due to the negative attention. Michael ended up accelerating the very thing he was trying to prevent.
Creatures Who Came on Sunday. Frank Hardy is so determined to find out what happened to Sharon's missing boyfriend that he not only ignores three back-off warnings from the local sheriff, supposed government agents, and Sharon herself, he then ends up leading mob killers (masquerading as those government agents) onto the boyfriend, who is in the Witness Protection Program and in hiding in a facility up on the mountain. This results in the mob killers taking Frank, Joe, and Sharon hostage, then forcing Joe at gunpoint to lead them back to the facility to point the boyfriend out so they can shoot him.
Death Surf. Once more, Frank Hardy starts asking questions to find out more about a woman who's been killed in a drowning accident while he was wind-surfing nearby. Granted, he's doing so at the behest of the woman's father, but only to find out what the woman was like. Frank receives two back-off speeches that he's going too far, one from the owner of a bar where the woman worked and the second from his brother Joe, but Frank is so obsessed with finding out about the woman that he not only ignores the warnings and finds the woman is still alive...but has led a criminal who wants to kill her directly to her. Nice job, hero!
Hercules: The Legendary Journeys Hercules's blind hatred of the gods and eagerness to help humanity in opposing them causes him to several times make things worse when he tries to make things better.
In season 4, Hercules becomes a god to better help mankind while ignoring the political situation on Olympus. His focus on saving humans is used to distract him while Hera overthrows Zeus and seizes control of Olympus.
Hercules tries to prove the Norse God Balder is not invincible by trying to wound him with a dart without considering where said dart came from. It poisons Balder starting off Ragnarok and the death of the Norse Gods. Hercules tries to brush it off until he learns the Norsemen are more dependent on their gods than other humans.
Perhaps the biggest one, Hercules does not hesitated agreeing to help the Sumarian king/demigod Gilgamesh in stealing a magical chalice that sustains the Sumarian gods since he assumes the Sumarian gods are no different than the Olympians and pointlessly tormenting humanity. In truth, the "torments" were fall out from their struggle to keep the evil Dahak out of the world. The destruction of the chalice, made only possible thanks to the help of Hercules results in the death of Iolaus, destruction of the Sumarian pantheon, and allowing Dahak to enter the world.
Had two in a single episode now (though one got started a few episodes prior): Arthur Petrelli is able to get off life support by stealing Adam's healing power — which he had easy access to because Angela sent Hiro and Ando off to release Adam in a bid to stop Arthur's schemes. Later on, Peter storms Pinehearst on his own, finds Arthur there, and subsequently gets his powers stolen.
According to Angela Petrelli, Future Peter was responsible for Sylar acquiring Claire's healing power. As Angela put it, "She had a very bad day."
The season 1 episode where Isaac tries to shoot Peter, in an attempt to prevent him from becoming the human nuclear bomb seen in the future paintings. When Peter becomes invisible, Isaac shoots at a noise behind him...and accidentally kills Simone, who wanted to help Peter.
When Sylar tries to kill Elle, she renders him unconscious with a massive blast of electricity. Unfortunately, she also overloads the Level Five power grid, allowing all of the super-powered prisoners to escape.
Nathan Petrelli initiates a government program to round up persons with superhuman abilities in order to protect regular citizens. But he is forced to flee when he is revealed to have an ability. As a result, Emil Danko takes over the operation; unlike Nathan, he wants to kill all so-called evolved humans, viewing them as nothing but animals. Not only does Danko murder Daphne Millbrook and (almost) Traci Strauss (although she returns in the next season and was also hinted to have survived in the episode itself), he then enlists Sylar to help him carry out his nefarious plans!
Then there's the Charlie issue. Hiro decides he can't save her life as she's already dying, so forgets about her, as do the writers. But at the very least he could have saved her from being killed by Sylar instead of allowing Sylar to take her ability.
He fixed it in the fourth season though.
How did Samuel Sullivan find out about the nature and true extent of his powers? Because Mohinder opened a box with research that his father expressly wanted never to surface and traveled all the way to his carnival of horrors to blab about it, of course. It's almost as if the writers hate his character too and wanted to give even newcomers a reason to hate his ass.
Foreman destroys a woman's immune system since they suspect its cancer, but she's still dying. Turns out all she had was a simple staph-infection and destroying her immune system doomed her. Good job, Foreman, thinking the worst instead of the routine questions and diagnoses of infections.
They also once cured a patient only to find out that he was a serial killer. Had their research skills been up to snuff, they could have taken certain obvious measures.
A particularly nasty one occurs in the Season 6 premiere. Upset at the way a mental patient who believes he's a superhero is being treated (the doctors trying to convince him his "superpowers" weren't real, House decides to take him out to a carnival and take him on a ride that lets him "fly". This culminates in the guy actually believing he can and jumping off a building. Even House himself is devastated and admits that he's responsible.
House of Anubis: Eddie and KT using the Staff of Osiris- which unleashes Ammut, the same goddess they were trying to prevent from being unleashed. It's kind of fair because the villains have tricked them into thinking the staff would stop Ammut, however, they did nearly help said villains destroy the world.
JAG: In the season four episode "Innocence", Harm first thinks that hes made a deal with the Japanese prosecutor who smiled and bowed in a friendly manner. It turned out that he had been greatly offended and had contacted the Japanese Prime Minister who told the press that U.S. Authorities were uncooperative and obstructive, and thus forced them to hand over the suspect to Japanese authorities.
Jericho: Jennings & Rall and Ravenwood are getting their hooks into the US government, even going so far as to suborn a plan to safeguard Russian nukes. John Smith decides the best way to fix things is to set the bombs off in cities containing J&R's branch offices and central HQ.
Kamen Rider Decade: If we are to make sense of Wataru Kurenai's contradictory babblings, mentioned that the eponymous Rider has to kill all the Riders to prevent the merging of the Alternative Rider Worlds, mentioning that "creation cannot begin without destruction". Instead, Decade chose to help all the Riders defeat their respective monster enemies as a Rider should. Cue Dai Shocker (the coalition of all the enemy organizations and monster races) through Apollo Geist becoming able to speed up the destruction of the Alternative Rider Worlds. Thankfully, Decade eventually turned into his nasty, somewhat evil Fury Form after being given a major beatdown by the original 9 Riders for all his troubles, thus being able to kill all Riders, trap them into cards and allowing the worlds - fallen riders included - to be rebooted to their proper states, but what the hell, Heroes?! What did they really have to do?! There was a lot of Mind Screw going on, but it seems attacking Decade was simply to goad him into becoming Decade Fury so that he would do what needed to be done.
The crossover between Decade and Samurai Sentai Shinkenger is this as Kaito steals the Ika Origami, forcing Genta to chase him down. In the process, the two encounter an Ayakashi named Chinomanako, who ends up stealing Kaito's Diendriver and becoming a corrupted Kamen Rider. Since the World of Shinkenger/Super Sentai World is "The World Without Riders", this is a big problem. Tsukasa and the Shinkengers have to pretty much bend Kaito backwards to get him to give up the Ika Origami so they can go and get Diendriver without him trying to run off with both.
Kamen Rider Fourze: In The Movie, the heroes get recruited by a secret government organization to stop the evil Space Ironmen Kyodain from attacking Earth with a Kill Sat, and are chased the entire way by a Dark Action Girl. On the Kill Sat, they use explosives to destroy a number of power stations...but only too late do they find out that their benefactors are the Kyodain, and what they blew up weren't power stations but Restraining Bolts that were keeping them locked in human form, and now they're free to attack the planet. Gentarodoesn't take it well.
He wanted to save Kuroto Dan, so he used his reprogramming ability to remove his resistance to Bugster virus. That in turn allowed Pallad to kill Genm by infecting him with massive amount of the virus. Then again, he didn't know Pallad was going do that.
Then he did it again by smacking Pallad with a Maximum Critical Finish while they were sharing a body through 'Double Action Gamer'. This allowed Pallad to reprogram himself to steal a copy of Emu's DNA, making him compatible with the Gamer Driver.
Law & Order: In the episode "Gov Lov" (the spelling is correct), Jack McCoy needs the husband of his male suspect to testify, but fears that the husband will take advantage of laws that allow spouses refusal to testify against each other. He's so determined to get the guy that he campaigns for, and succeeds in, nullifying all gay marriages in the state by reestablishing the "one man one woman" definition. It completely backfires when the husband admits, in a courtroom full of people, that he would have voluntarily testified against his husband, but now that McCoy had effectively ruined hundreds of marriages for his own agenda, he would refuse, even though he would be arrested for contempt of court.
The television adaptation of Terry Goodkind's Sword of Truth series, this trope is played at the conclusion of Season 1 and leads into Season 2 - although Big Bad Darken Rahl is defeated, Richard & Co have inadvertently "broken" the ground, opening a rift to the Underworld. Darken Rahl is revealed to have made a contract with the Keeper of the Underworld a while ago, and now serves as the Keeper's right hand man in his attempt to kill even more people than before. The Keeper, after all, hates all life. Darken Rahl also has the power to manipulate people even better than before - by offering dead souls the opportunity to live again if they agree to kill more people for the Keeper.
Also done earlier. Two of Rahl's soldiers have had enough of Rahl's tyranny and have the perfect opportunity to kill him, as one of them knows Rahl personally. Then come Richard and his crew and kill the one who was supposed to do the killing, assuming him to be a loyal soldier. Only Richard gets to kill Darken Rahl! Don't mess with the prophecy.
The Legend Of William Tell Vara, trying to escape from the group, falls over a cliff. When Will rescues her, she knocks his crossbow down into the ravine, leaving them defenceless.
Lexx: The destruction of Fire at the end of Season 3 leads directly to the destruction of Water, and then the subsequent flooding of Earth with the reincarnations of everyone who had been sent to Fire (Hell).
In the fourth episode of the original show, the cops stop taking bribes from and arrest the city's biggest crime lord. The remaining season and a half is spent trying to stop new, more ruthless gangs from getting a foothold.
In the fifth season, Ben thought that by killing Locke, he would be able to get back to the island, but that unleashes Jacob's nemesis. Ben then kills Jacob thinking he's being instructed by Locke, but has unleashed more terror again.
Not to mention moving the island at the end of season four. That resulted in rampant time flashes, and was the entire reason Locke had to leave the island in the first place.
Season 2 finale: Locke does a HeelFace Turn and decides the button doesn't need pressing. Cue "I was wrong".
The Season 5 finale is a massive moment one for almost all of the characters at once, but mostly Jack, Daniel, and Juliet. They plan to detonate Jughead, the nuclear bomb, in order to change the future, but blowing up the bomb causes all of the futures they were trying to prevent. Because of their plan, Juliet is called to the Island to deal with the Incident that the bomb caused, and the chain of events that leads to Oceanic 815s crash and, subsequently, the frieghter being called, is set in motion.
While were at it, Desmond abandoning his post to chase Kelvin across the Island means that hes not there to push the button in time and causes an electromagnetic incident that causes the plane to crash.
Against Jacks protests, Sawyer tries to disarm a bomb the Man in Black snuck onto the submarine. Because of this, the rules that prevent the Man in Black from killing the candidates are void and the bomb will now actually go off. The resulting explosion kills Sayid, Jin, and Sun.
MADtv: Played with in one sketch featuring The Eracists, a children's vocal group dedicated to combating racism. In the sketch, they walk in on Yasser Arafat and Benjamin Netanyahu just as they're about to sign a peace treaty, and decide to sing them a song. Unfortunately, the obnoxious, Glurge-filled song only gets Arafat and Netanyahu angry at each other again, and they declare the peace treaty off. Upon hearing this, the Eracists offer to sing them another song... and they promptly sign the peace treaty.
Malcolm in the Middle: In one episode, Reese was taught a lesson and gave up his bullying ways. This of course resulted in a bunch of lesser bullies turning the schoolyard into chaos and even abandoning standard ground rules, like not picking on the crippled kid.
Merlin (1998): Merlin does this by recruiting Lancelot as the king's champion, who manages to completely screw up the relationship between the king and queen and provide Mordred with just the opportunity he needs to start a war and attempt to take over. All because he misinterpreted the Lady's message (who was, of course, unnecessarily vague) and assumed Lancelot was the knight he needed. Turns out it was his son Galahad. You know, the son who is now an orphan because his father abandoned him and his mother committed suicide.
In Merlin (2008), our hero, under the advice of others, kills Morgana for the "greater good". And although it's a Disney Death, when she comes back it's made clear that this action is a major contributor to Morgana - up till now depicted as a good guy - going to the dark side.
He also releases the dragon, even though it's clear the reptile is less than trustworthy.
Monk: "Mr. Monk on Wheels": A boy steals a bike, but then while riding off with it, hits a pothole, flipping himself over and sending him sprawling in the grass. Quite by coincidence, Monk and Natalie are walking through the office park when the accident happens, and Natalie, seeing the accident, walks over despite Monk's protests and helps the thief to his feet, even fixing the chain, and sends him on his way, this whole time unaware that the bike is stolen. Only once the legitimate owner of the bike comes running out of the nearby building does Natalie realize her mistake, and she is visibly embarrassed by this. It gets worse when Monk gets shot in the leg while knocking on the door of the thief's house.
Crow also has this reaction to the revelation the Planet of the Apes-esque Earth of 2525 they're orbiting at the start of the season is the result of Mike's descendants marrying simians.
Then there's the time Crow went back in time so Mike doesn't go into the temp agency. End result? Mike dying as he's rising to rock star fame and his Jerkass brother being shot up onto the Satellite of Love.
And then there's Joel, who built the robots...out of the "special parts" used to start or stop the movies.
Once Upon a Time: A horrible example for Prince Charming. Trying to get water from a healing lake to heal the beloved of his unwilling fiancée Princess Abigail, he kills the siren guarding the lake. When his mother is mortally wounded, he goes back to the lake only to find that it's dried up because of the death of its guardian, and his mother dies.
On The Orville, a time travel incident allows Kelly the chance to never go on a second date with Ed. She thinks she's sparing Ed the pain of how their marriage will end with Kelly cheating on him. But this also means Ed never captains the Orville with Claire, thus creating a new timeline where the Kaylons manage to wipe out half of life in the galaxy. Ed chews Kelly out for not considering the ramifications of changing history and Kelly is forced to admit he's right.
The Outer Limits (1995): Happens in almost all episodes. For example "The Light Brigade": While humanity is at war with a powerful alien race, a last desperate attempt is made to carry a huge bomb to destroy their home planet. After finding and killing an alien in disguise, the heroes release the bomb and discover the alien turned the ship around—the heroes just bombed Earth.
In Outlander, "Black Jack" has Jamie captured. Jamie is under sentence of death, but Black Jack makes the offer: Have sex with me, and I'll kill you however you like, instead of the gallows. Jamie tells Black Jack to go to hell. Then Claire stages a daring rescue—and gets captured. Jamie has to agree to Black Jack's terms to get Claire released.
Person of Interest: In one episode, an investigative journalist caused a man's death and put her own life in danger when she accused the man of being a criminal mastermind based on faulty intel.
In Power Rangers RPM, Dr. K was being imprisoned unjustly by the government so they could use her as a researcher. She uploads a computer virus into their systems, and is apprehended by secret agents before she can install the firewall. The virus goes on to nuke the planet, wiping out pretty much all ecosystems, and either killing or enslaving every human not in the Domed Hometown of Corinth. Doctor K manages to escape thanks to some friends bailing her out. Nice job getting your freedom, doctor. Nice job protecting America, secret agents.
One of these in the backstory leads to the events of Power Rangers Ninja Storm. The main villain was initially just a power hungry ninja. His clan banished him from Earth. He came back as a power hungry warlord with alien technology. Oops.
And it wouldn't even have happened if Cam hadn't gone back in time and exposed said ninja as a traitor. It doesn't help that said ninja was his uncle.
And for a hat trick of "smart people doing dumb things", we go to Power Rangers: Beast Morphers. A young Nate Silva was messing with Morph-X, snake DNA and old Morphers in a way to get them to work differently. All of them failed until he used a Cell Shift Morpher. Specifically, Scott Truman's Cell Shift Morpher still infected with the Venjix Virus, the same one Dr K. made. The two bonded with what was inside, and they all went into Grid Battleforce's computer systems. The result of all this? Evox.
Solon tries to help Amelia and Ollie against Void Knight by throwing them a key to activate the Hengemen, only for Void Knight to intercept the key and claim the foot soldiers for his own use.
Zayto ends up releasing the Sporix by accident when his Dino Dagger gets deflected into the chest containing them.
Prison Break: Michael does this several times, but special mention can go to when he starts the riot at Fox River, leading to several deaths (for him to feel guilty about) and T-Bag finding out about the escape.
In "Pilot", Danny Matheson tries to prevent his father Ben from being taken by the militia. This results in one militia being killed, as well as the deaths of Ben and four villagers.
In "Chained Heat", Charlie Matheson persuades Miles not to kill a bounty hunter that has attacked the group. A few scenes later, said bounty hunter sics the Monroe militia on them.
In "No Quarter", the rebels hand over Miles Matheson to the militia when they find out that Miles helped to create the Monroe Republic. Subverted Trope, when they come to his rescue afterwards.
In "The Plague Dogs", Danny decides to rescue Tom Neville from being buried under a lot of rubble. He gets arrested again for his trouble.
In "Sex and Drugs", Charlie is given the job of murdering a former cop on behalf of a drug lord. Defied Trope, because Miles prevents her from doing the deed at the last minute.
In "Ties That Bind", Team Matheson decides to save Mia Clayton, Nora Clayton's little sister. Big mistake, because it turns out that Mia is a bounty hunter and mole for the militia. She gets the pendant from Aaron, and it gets delivered to Philadelphia, the Monroe Republic's headquarters.
Rachel's initial confession about the pendant in "Soul Train" ends up with a succession of Oh, Crap! moments for her in "The Children's Crusade" as she discovers just how single-mindedly obsessive Bass Monroe is. She could be considered directly responsible for the capture and torture of Dr. Jaffe and indirectly responsible for the capture of his daughter, since Bass apparently got the idea from capturing Rachel's family and thus spotting her weakness. In "Kashmir", she tries to construct a bomb disguised as a power amplifier. Unfortunately, she gets found out, and Monroe threatens to replace her with Dr. Jaffe. So Rachel kills off Jaffe to save her and Danny's lives.
In "Nobody's Fault But Mine", Team Matheson rescues Rachel Matheson and Danny. Unfortunately, Monroe now has a working power amplifier, which he uses to activate a fleet of helicopters.
In "The Stand", Danny dies stopping the helicopters. The Monroe Republic unfortunately gets more pendants, scientists and resources from Randall Flynn.
In "Ghosts", Miles and Nora manage to recruit Jim Hudson to their cause, but they wreck up his life in the process.
In "The Song Remains the Same", Charlie prevents Rachel from murdering Tom Neville. Tom Neville subsequently escapes and kills off the preacher Nicholas in the process.
In "Home", Captain Dixon tries to shoot Monroe, but he kills Emma Bennett and wounds Monroe instead. Miles kills him off without a word for that.
"The Night the Lights Went Out in Georgia" has Team Matheson stop a nuclear bomb from exploding in Atlanta, Georgia, and they make sure Georgia doesn't get to use the bomb. "The Love Boat" has Team Matheson rescue Dr. Ethan Camp (a scientist being made to produce smallpox for Monroe) and his family, and they make sure they escape somewhere where they won't be found. Unfortunately, those decisions come back to haunt them in "The Longest Day", when Monroe uses drones to kill off 270 out of 300 men in one drone strike.
In "Clue", Miles's decision to recruit Jim Hudson comes back to haunt him. The guy is still bitter about his life being wrecked up, he was responsible for the 270 men killed off, and he nearly kills off Miles before Jason Neville kills him off.
In "Children of Men", Rachel tries to be a suicide bomber on Monroe, but the attempt fails. As a result, she ends up bringing the Monroe militia and Randall Flynn into the Tower.
In "The Dark Tower", Team Matheson succeeds in turning the power back on worldwide. But it turns out that they played into Randall's hands, and he launches Intercontinental Ballistic Missiles at Philadelphia and Atlanta before shooting himself in the head. Not only that, but the American government he's working for is now going to return to the USA and retake what's theirs.
Kate tries to rescue her brother, and he ends up dead in her arms. It's worse than it sounds: she abandons the other outlaws who are ready and willing to help her, sneaks into the castle by herself, is captured in under five seconds, and watches her brother die as he tries to save her. And then for some inexplicable reason, the outlaws let this idiot join the team, giving her ample opportunity to endanger their lives in almost every single episode that follows.
In the episode "Too Hot to Handle" the outlaws steal Prince John's supply of water in order to help villagers struggling through a drought. Because they're all idiots, they dont bother to hide the water barrels that are clearly marked with John's insignia. When Prince John turns up and discovers the barrels in the middle of Locksley, he drowns a man in the drinking water. Thanks, heroes.
Everyone treats the mentally-unhinged Isabella like crap, and then they look surprised when she goes mad and starts killing everyone.
In the Run For Your Life episode "Down With Willy Hatch", Paul's friend Willy (a stand-up comic) is framed for statutory rape, not the best thing for a man on the verge of a nervous breakdown. Paul clears his name and convinces Willy to take to the stage... but when he bombs, Willy's no longer just on the verge of a nervous breakdown.
In the Shadowhunters episode "Raising Hell", the protagonists and Magnus Bane summon a memory demon - containing it in a bond they form by linking hands, but each of them has to give up a memory of "the one they love the most" in order to get Clary's memories from the demon. Alec freaks out when he has to give up the memory of Jace, since he's desperate to deny any sort of romantic attraction. He breaks the bond, despite Magnus' explicit instructions not to do that. This forces Clary to kill the Memory Demon to save Jace, costing her the chance of recovering her memories.
Sherlock: Nice job going in the cabbie, Sherlock. You put your life at risk. Now John has to save your rear end.
Nice job trying to deal with the gangster, genius. Now you're going to get strangled.
Ugh. Here we go again. Sherlock, you're untying John and Sarah with the dude that tried to kill you? Uh...
Seriously, Sherlock. You're trying to box a professional killer, and you're bloody-awful at it.
Good going breaking into Magnussen's apartment, Sherlock. You indirectly saved his life and now he has even more blackmail material on you and your friends.
Thanks a lot, Mary. Wait until John finds out you shot his best friend.
Nice going, geniuses. You didn't realize that Mary was an assassin from the CIA.
Smooth move, genius. You didn't realize Magnussen knewJohn was your pressure point.
Nice job shooting Magnussen in front of everyone, Sherlock. Now you're going to get arrested or sent on a suicide mission.
Sliders: So you and your friends have arrived in an alternate San Francisco where an asteroid is on a collision course with the City by the Bay ("Last Days"). No prob: just send a nuclear missile out to blow it up... except in this universe such technology hasn't been invented. Luckily you can give them the key to inventing said tech, and do so, thereby saving the day. Now all you have to do before you leave is to make sure the formula is destroyed so no one else can do it, and keep this particular universe free of one of the most devastating ways to kill people in history... uh-oh.
Our heroes woke up the Wraith, inflicting them upon the galaxy and angry because of the lack of "food" (humans). The Wraith were always bad news, but their newly accelerated schedule has resulted in many worlds wiped off the map, and everyone working on a way to stop them finding out they have a few decades less than they thought. Not that they stood a chance in hell, mind you, but they could at least have built up their populations enough to weather the culling.
Next is the Genii, one of those working on a plan to stop the Wraith, flawed though it was. Mistrust on both sides made them enemies for the better part of two seasons, up until a new leader came into power. All because they were trying to trade C4 as "farming tools"...
Then they turn a Wraith into an amnesiac human. He starts to turn back, but not all the way, and so once he remembers who he really is and escapes, he finds his people no longer want him now that he's half-human. By now, he's out to overthrow humans and Wraith and have the other human-Wraith hybrids he's created rule. He didn't hate humans that much, though, until our designated heroes betrayed him further, though.
Then they turn the Replicators against the Wraith... and the Replicators decide that the best way to fight the Wraith was to attack their food supply (of course, they may have done this out of spite because they already hated humans and Ancients).
In short, all three major threats to humans in the Pegasus Galaxy were created by the Atlantis team. They really, really should have just stayed at home.
It was even lampshaded when the combined peoples of the Pegasus Galaxy put Sheppard's team on trial for doing all of this, and call them out on every single mistake mentioned above. The trial, by extension, was to convict the Atlantis expedition as a whole, but they were smart enough to realize trying to tackle that beast directly was not going to end well. During the trial, Sheppard and Woolsey do make the point that, while the Atlantis expedition did screw things up pretty bad, they've also been risking their lives trying to fix their mistakes every since. Without them, there's a good chance the Wraith would have kept on culling humans without strong opposition indefinitely.
The Ancients also did a good Neglectful Precursors work, as they accidentally created the Wraith, then developed the Replicators as a weapon against them. When the Replicators couldn't do the job, they wiped them out but missed some, hence their continued existence in the present. They shouldn't even have lost the war with the Wraith with the first place; they were too stupid to realize what "overwhelming odds" means and ended up giving their enemy the necessary tools to clone a massive army and Zerg Rush them into defeat.
Every time they defeated a Goa'uld, another, even more ambitious one rose to take his place in the resulting Evil Power Vacuum. This only stopped when the Goa'uld were overthrown as a whole.
Unfortunately, the SG-1 team wasn't content to rest on their laurels. Instead, they hunt down some old Ancient technology, get transported to another galaxy (sort of), thus allowing the Ori (evil ascended beings) to move in. In effect, after killing off the evil false Gods, the SG-1 team invited evil real "gods" to move in.
The basis for the franchise really. Movie - Unburied the gate, went to Abydos, unintentionally informed the Goa'uld that the gate on Earth had been unburied and thus Earth was within easy access for them. Killed Ra, everything is good. TV Series - Oh shit, you created a power vacuum. The goa'uld are fighting and they know the Earth stargate is unburied. And you've proved yourself to be a viable threat to their power and therefore put Earth in danger. Nice job.
Their MacGyvered dialing computer is well known to be dangerously flawed, lacking key safety protocols, and sucks up power like there's no tomorrow - on the order of $1 billion dollars just to turn the lights on. It was the cause of countless disasters which wouldn't have occurred had they had a proper DHD. Yet in all their travels they never once thought it would be a good idea to get their hands on one, or even hook up the one found with the Antarctic Gate if for no other reason to use its power crystal instead of the expensive base electricity.
This trope is lampshaded in the 200th episode, along with everything else.
Carter: It makes the characters look stupid. I mean, do you really think the best way to introduce the heroes of the story is to show them causing a massive catastrophe? Mitchell: That's... realistic.
Stargate Universe: The crew avoided making a mess for nearly a full season. Then after learning of a potential spy, they along with SG-1 alum launch a poorly-planned undercover mission that ends with Rush in the Lucian Alliance's hands. As a result of gaining his knowledge, they are able to connect the Stargate and there is now an entire enemy force on Destiny.
In "Mirror, Mirror", Kirk and company go to the Mirror Universe, and Kirk gets Mirror Spock to try reforming The Empire. So he does. When next we visit it, it turns out that the reforms made weakened the empire to the point of being unable to defend against the Klingon/Cardassian Legion of Doom. Humans and Vulcans are now slaves. Way to go, Jim. (This gets retconned into the Expanded Universe as Spock playing out a really longBatman Gambit; he could have made reforms without weakening the Empire, but he didn't believe they'd last beyond his death.)
"The Devil in the Dark". Turns out that monster you shot? It was an alien nanny who was only acting in defense of the nursery. And those weird stones that you've been trying to crack open? They're the babies.
At the start of the episode "The High Ground", Doctor Crusher uses her Doctor's Orders to demand to stay at the scene of a terrorist bombing to help, in spite of the dangers it presented. Naturally, she's quickly kidnapped, setting in motion events that nearly sees the Enterprise destroyed, almost brings the hammer of the Federation down on the planet, causes the deaths of several crewmen as well as the Well-Intentioned Extremist terrorist leader, and does nothing but add to the already unstable political climate of the planet they're on. Yay morals?
Not the most heroic example, but "Force of Nature" has a good one: Two Hekaran scientists try to warn Picard and his crew that the use of warp drive near their planet could cause a dangerous subspace rift. Their theory is possible but still unprovable, and Picard decides to recommend further research, but the female scientist gets fed up and decides to prove the theory herself—by blowing up her own ship to generate enough energy to create the rift. Yes, she proves her theory, but she creates the very rift she had sought to prevent, thus endangering a nearby disabled ship and making it harder for the Enterprise to rescue the crew, not to mention the environmental changes to her planet because of the rift.
In "The Ship", Sisko and a Vorta enemy share the blame. Sisko wants a crashed Dominion ship, and the Vorta wants to rescue an injured Changeling. But because both refuse to negotiate or trust each other, this leads to the deaths of the Changeling, the Vorta's Jem'Hadar, and most of Sisko's landing party.
A Romulan senator also accuses Sisko of essentially causing the entire Dominion War because he mishandled their first few meetings. The senator was, of course, rather naive in assuming the Dominion could be negotiated with effectively. Of course, Sisko and Garak then used the senator to break the peace between the Dominion and the Romulan Empire. Initially by providing him with fake evidence of impending Dominion attack on Romulus, but when that failed Garak went behind Sisko's back and murdered the Romulan senator while making it look like the Dominion was responsible.
Starfleet officer turned Maquis leader Eddington is captured before the Maquis are wiped out by the Dominion. Freed to help on a mission, Eddington argues that his friends died because he wasn't there, saying the Maquis had the Cardassians beaten and about to achieve victory. Sisko fires back that all the Maquis did was make the Cardassians desperate enough to join the Dominion and thus stronger than ever.
Eddington: We had the Cardassians on the run! Sisko: And they ran straight to the Dominion!
The Voyager crew end up presiding over a case of a member of the Q Continuum who wants to die, thus seeking asylum on the ship so that he could die in peace. His wish is granted when Janeway grants him asylum and he dies shortly afterwards. As a result, the Q Continuum undergoes a major upheaval that results in a civil war with potentially disastrous ramifications, both within the Continuum and throughout the entire galaxy.
When the ship is taken over by Hirogen and the crew are used for holodeck recreations, Janeway and the Hirogen leader come to an agreement (in contravention of the Prime Directive) to trade holodeck technology for the ship and crew's freedom. The idea was to allow the Hirogen to conduct holographic hunts of sentient creatures instead of real ones. A season later, we find out they deliberately used it to create basically a race of fully aware, pain-feeling holograms. Which in turn leads to a hologram rebellion under a holographic cult-leader/terrorist who wants to wipe out organics.
On a world where the species' third gender is subjugated, Trip encourages one of them to resist, and this results in their death. Following this, Archer gives Trip a Nice Job Breaking It, Hero! speech about how this wouldn't have happened if he'd let things be.
At the end of season four, Sam has spent most of the season getting the power to kill Lilith so he can stop her from breaking the final seal and freeing Lucifer. Turns out, Lilith was the final seal, and by killing her he opens Lucifer's Cage and begins the Apocalypse. Oops.
At the end of season six, Castiel absorbs all the souls of Purgatory to get the power to defeat Archangel Raphael, who wanted to restart the Apocalypse. In doing so, he goes insane and unleashes the Leviathans, creatures that God locked away to stop them from eating everything else, who become season seven's Big Bads.
To an extent, Dean as well, not only for breaking the first seal between seasons three and four but also for revealing to Azazel that his plans were going to work before he'd even put them in place. Okay, so Azazel was possessing his grandfather at the time and Dean thought he was going to save his mother, but it caused the death of his grandparents and father and Mary's resulting deal: Mary gives Azazel permission to enter her house in 10 years in exchange for resurrecting John. This deal is what kick-starts the plot of the whole series.
Taken: In "High Hopes", Jesse Keys suggests to his father that they take what they know about the aliens to the Air Force. He is eventually able to track down Owen Crawford, thereby exposing his family's existence and the aliens' interest in them to the UFO project. This has serious consequences in both the short and long term. In the short term, Russell is killed the next day when the implant in his frontal lobe is removed. In the long term, Jesse's decision to approach Crawford leads to the Keys family being hunted by the project for the next 40 years.
Teen Wolf: Scott is well-meaning in his desire to help Jackson and does not want to kill him or let Derek do so. However, by protecting Jackson, he technically bears some responsibility for the murders that Jackson subsequently commits as the Kanima, including a fair-sized chunk of the Beacon Hills Police Department.
Obviously, the corporation behind the time machine in the first place, as thanks to them the Hindenburg crashed a day later and only killed two people, thus affecting history.
The end of the pilot has Lucy at first thinking things are better as her sick mom is okay. However, she then finds out that not only is she engaged to someone she's never met, but her sister Amy was never born.
Titus: Subverted Trope in the episode "Titus is dead". After the main character finds out that his dad who has been divorced five times is dating again, he tries to convince his dad to break up with his new girlfriend. After talking to each other, Papa Titus proposes to his new girlfriend, instead of breaking up with her. Nice job fixing it hero.
Torchwood: Generally speaking, the problem in any given episode was probably caused by them at some point:
In "Day One", on Gwen's very first day on the job, she tossed a screwdriver, accidentally breaking open an alien meteor and leading to the deaths of Carys' friend and ex-boyfriend as well as an entire sperm donation center.
In "Cyberwoman", two people were killed and the whole planet was put in danger because Ianto secretly stashed his Cyberman girlfriend in the basement.
In "End of Days", Owen Harper's opening of the rift rescued his boss and his best friend from being trapped in the wrong decade forever, but it also caused a wave of anachronisms including ancient soldiers in the streets and an outbreak of the bubonic plague in Wales. This despite Ianto practically begging Owen not to open the rift, and even shooting him to try to prevent it. Instead of learning from this colossal mistake, the rest of the team eventually side with Owen and do the exact same thing, again, to flush out the results of the prior opening. Which works, but unleashes Abaddon. Predictably, things get worse before they get better.
Not to mention how it nearly killed everybody in "Dead Man Walking" and did kill 12 people.
All those problems with Captain John Hart would have been avoided if it weren't for Jack simply being there.
In Torchwood: Children of Earth, Jack and Ianto have gone storming into the alien's base guns blazing in order to, erm...threaten it, pissing it off enough to release a deadly virus, killing everyone in the building, including Ianto.
The really hilarious irony being that Torchwood was originally founded by Queen Victoria because she felt that the Doctor brought too much trouble in his wake!
Touched by an Angel: A man wakes up from a twelve-year coma. He got in a car accident because he used his wife's car instead of his own. He got in his wife's car because he couldn't find the key for his own. He couldn't find the key for his car because Monica was holding it so she could look at the angel keychain...
One of the most direct examples from the first season. At the end of "The Day That Wasn't", Five steals some information from The Commission and then time-travels to where the episode began, setting up the timeline we follow to the finale. In the original timeline, the whole family is doing much better emotionally, and Vanya discovers Harold's machinations much earlier It's entirely possible that Five's meddling is directly responsible for the Apocalypse.
In the penultimate episode, Luther finds Vanya genuinely distraught, believing she killed Allison in a fit of rage. He knows it was an accident, but he's mainly thinking that the girl he loved almost died. Because of this, he chokes Vanya unconscious and locks her in the anechoic chamber in the basement, not knowing that this will cause her to snap and go on a world-ending rampage.
In the final episode,Allison is slowly walking towards Vanya, who smiles upon seeing her. Just as it looks like Allison can talk her down from ending the world, Luther and Diego charge her, driving an already unreasonable and emotionally unstable Vanya completely off the rails and destroying their last chance to save the world.
Hargreeves arranges his death to bring the family together to prevent the apocalypse. This leads to Klaus stealing the case, which sets in motion the events which cause the apocalypse.
Unsere Mütter, unsere Väter: On the Eastern Front in 1943, Wehrmacht officer Wilhelm Winter tells a superior officer that partisan activity has increased, and the officer drily replies "Thanks to our far-sighted policy of treating these people as inferiors."
The Vampire Diaries: Stefan screwed up BIG TIME in season seven. First, while Damon wanted to wait until Lily's guard was down and kill Julian after six months, Stefan, who was justifiably pissed that Julian had killed his unborn child, went after him immediately instead. This action caused Lily to put a spell linking her life to Julian's. As a result, when she later tried to kill Julian herself, it was too late: Julian had removed the spell, fearing that he would die soon at the hands of her kids, and didn't want her to get killed along with him.
Later on, Stefan led a revenge mission with Damon, only to nearly get killed by Julian and his friends. Now, Damon wanted to stop. However, Stefan didn't listen and teamed up with Valerie, the mother of his unborn child who also wanted Julian dead, to kidnap Mary Louise. Unfortunately, Stefan told no one else what he was doing. This led to Julian and Nora thinking that everyone else was involved, and both Bonnie and Damon were attacked. The end came with Damon AND Stefan both trapped in the Phoenix stone.
Nice job not keeping your mouth shut JUST to try to prove that Beck got his line right, Tori. Too bad it made the Jerkass lead star not approve of you or him.
And in "Locked Up", when the chancellor is about to free Tori, Robbie knocks his electric clock into his octopus' tank, which zaps it and kills it. And then they're all in prison with her.
Although, Tori does end up fixing things. She (accidentally) gets the Jerkass lead star hospitalized, which not only gets Beck his role back, but also makes everyone else on the set happy because they all hated her.
On The Voice, judge/coach Seal came down hard on contestant Kiyomi Vella for having a "backup plan" in case her musical career didn't pan out (Vella was attending university to get an environmental science degree, something that would give her an income while she pursued her musical dreams). The scolding shamed Vella so much that she quit college to concentrate on music at his urging. And then she was eliminated from the competition. As of this writing, neither her musical career, nor her attempts to get back into college, has been all that successful. Good job, Seal. Really good job.
Dr. Bernard insists Jeff not getting the vaccine after he's bitten, almost resulting in him dying from rabies. Admittedly, he didn't know the vaccine would work and thought he was protecting Jeff against further damage.
Olivia attempts to take Jeff back to the lab and only succeeds in raising the security around his room after she's caught, almost preventing Pasteur from being able to administer the vaccine. Bogg, infuriated, calls her on this.
The Walking Dead: Michonne killing the Governor's zombified daughter. Whether you think his and Milton's attempts to try and heal her were futile or not or whether you think he deserved it or not for kidnapping Glen and Maggie; the fact remains that beforehand the Governor was far closer to a Shane-style villain. Killing others to secure their stuff, interrogating people using violence etc. Afterwards however he became a full on psychotic Bond-villain that eventually leads to the deaths of Merle, Andrea and about a dozen Redshirts
In Wheeler Dealers, due to Edd China repainting the 1967 Mustang in S 09 E 14 and outfitting it with aftermarket parts, the car had lost its desirable "A-Code" (vehicle with mostly original parts) status.
In The Wiz Live! Dorothy's crash landing in Oz kills Evamean, the Wicked Witch of the East. While the Munchkins thank Dorothy for freeing them from Evamean's control, the Wiz unfortunately tells Dorothy that Evamean's death left the whole East portion of Oz free for the taking. After the Wicked Witch of the West, Evillene, claims this property, and enslaves its denizens, the Wiz sends Dorothy to kill Evillene, before the witch takes over all of Oz.