Nice Job Breaking It, Hero/Comic Books

"Jenny Sparks: There must be something you can do. You're patriotic, well-read and an excellent communicator. Have you ever considered a career in local government? Do I even have to say it?: Politics? Actually, that might not be such a bad idea."
 * Happens all the time in Hellblazer; it's a fact of the protagonist's life that he never has any permanent, unequivocal victories.
 * Done on a universal scale by Reed Richards Is Useless. Reed learned some time ago that Galactus' existence, however problematic, is necessary to the universe. He tried to get around the problem by turning Galactus into a star. In mainstream continuity, this still ends up releasing Abraxas. In Earth X, it frees up the Celestials to overrun the universe (because what Galactus was really eating was their young, which gestate in planetary cores -- then hatch).
 * In Jenny Sparks: The Secret History of The Authority, we find out that a thirteen-years-old Jenny Sparks convinced a friend in Vienna that he was wasting his life making paintings that didn't sell and suggested that he'd find another profession.


 * This happens at the very beginning of the French comic book series Les Légendaires. The Five-Man Band confronts the Big Bad and foils the plot that should grant him eternal youth... but in doing so, they shatter the magic stone he was using, which results in a supernatural discharge that turns not only the heroes but all the adults on the planet into children. (As well as the denizens of the near-by Elfin World parallel dimension.) Unfortunately for the protagonists as they struggle to correct their mistake, their responsibility in this mess is common knowledge. Needless to say, they aren't very much welcome anywhere after that.
 * In an early Avengers issue, the team has come to a military base to locate the Cosmic Cube, an all-powerful wish-granting machine. They find Prince Namor the Sub-Mariner trashing the place for unrelated reasons. During the fight, Hercules tells Namor they'll never let him get the Cosmic Cube. Namor promptly escapes, leaving Hank Pym fuming -- he's guessed (correctly) that Namor had never heard of the thing until Herc told him. Naturally, Subby finds the Cube and comes back to mop the floor with them.
 * In Blackest Night, Hal Jordan managed to get all seven Lantern Corps to work together to fight against the Black Lanterns. Ultimately, they all fire their rings at the Black Central Power Battery, in order to destroy it.
 * Another Green Lantern example: When the Corps executed Sinestro in Green Lantern Corps vol. 1 #222, Sinestro transferred his soul to the Central Power Battery and imploded it from within (rendering almost all of the power rings powerless, with the exceptions of Hal, Guy and Ch'p), and that's when he discovered the yellow impurity (if we go by current continuity, that yellow impurity is Parallax).
 * In Booster Gold vol. 2, when he goes back in time to save his friend Ted Kord, the second Blue Beetle.
 * Almost and sort of happened in the Rock of Ages storyline in JLA.
 * Definitely happened in the Midsummer's Nightmare storyline (which caused that JLA incarnation to form in the first place): after foiling the Big Bad's plan, he explains he only did it to prepare humanity for a worse threat  that was still to come.
 * In the JLA's battle with the invincible supervillain the General, Batman tries to use hypnosis to defeat the villain. He did a good job until Superman comes bursting through the wall. Batman even yelled at Supes for the screw-up.
 * Sleepwalker has just about defeated the Ax Crazy Psyko and halted his rampage across New York. It's then that he sees a man who's possessed by a demon and uses his warp beams on the man to expel the demon, which provokes a watching Spectra to attack him. While Sleepwalker defends himself from Spectra, Psyko seizes the opportunity to escape and continue running amuck through New York. Fortunately, Spectra later fixes her mistake when she helps Sleepwalker bring Psyko to justice once and for all.
 * This is the premise that kicks off I Hunt Monsters when Willam Warlock inherits a graveyard that acts as a Sealed Evil in a Can to powerful monsters his ancestors trapped there. However, because no one told Will about this beforehand, when it comes time to recharge the obelisk keeping the monster dormant, he refuses to believe what going on and declines to help. Say the least, he regrets that decision a moment later when the monsters free themselves and go to wreak havoc across the world.
 * Raven screwed up big time in Teen Titans. During the one-year Time Skip (long story), she spent several months working on bringing her old friend, Joseph Wilson, back to life. She succeeded, and what was the first big thing Joey did after returning from the grave? Tried to murder the Titans. Thanks, Raven. What would we do without you?
 * Another Teen Titans example is when Damian joins the team. The Titans are fighting a rampaging teenage psychic. Raven is able to calm him down. Then the Boy Wonder kicks him, pissing him off even more.
 * Also happens in Marvel's Crisis Crossover Siege. The Avengers assemble in Asgard to defeat Norman Osborn, reuniting the 'Big Three' of Marvel; that is, Captain America, Iron Man and Thor. Osborn is defeated, but not before having the Sentry destroy Asgard. It then turns out that Osborn was the only one who could control the Void, the Sentry's evil side, who, as the president was informed, "has no limit to his powerset". The Void is then shown preparing to kill them all.
 * In a six-issue miniseries about Mara Jade, By The Emperor's Hand, Mara is sent to go assassinate a gang leader, and she does, then gets rewarded for a job well done. Only to find out, months later, that she'd killed a decoy, effectively faking his death and giving him that much longer of a rein.
 * For that matter, after the Emperor died Ysanne Isard, Director of Imperial Intelligence, pulled a Nice Job Breaking It Villain. She'd known Mara was an agent of some sort for the Emperor, but little more, and she'd been highly suspicious of her - so after the Emperor's death, Isard locked Mara up, thus turning her against the Empire.
 * An older (timeline-wise) example. The Jedi were so desperate at the Battle of Ruusan they were giving nine and ten year old children enough Force training to be dangerous, shoving lightsabers into their hands and sending them to be cannon fodder (Seriously, are we supposed to see the Jedi as good guys?!) One of those ten year olds falls out of an airship, apparently to her death...only to survive and be found by Darth Bane. Congratulations, your child conscript is the next Sith Lord!
 * At least two or three of Batman's rogues have been created this way as well, mainly by accidentally causing their downfall (at least one of the Joker's Multiple Choice Past stories have him being scared by Batman and then either falling or jumping into the chemicals that result in his current look, and in some adaptations of the Riddler's backstory, it's implied he once worked as a game programmer before Bruce Wayne fired him), both in the comics as well as in various adaptations of the comics. Nice job breaking it, Dark Knight.
 * Cassie may have managed to give Congress a glimpse behind The Masquerade, revealing the Soviet Rodinan ambassador as a literal monster and thereby striking a small blow in her fight against The Legions of Hell... but she apparently didn't anticipate that doing this at the height of the Cold War would be a perfect way to push the world right to the edge of nuclear war.
 * In this Chick Tract, the protagonist's aunt, who is a conservative Christian, and thus has an interest in seeing her nephew be saved, dies and leaves him all of her money. Unfortunately, said nephew hears the news right after he was witnessed to by another Christian and seriously considering conversion. It turns out that he was only interested in Christianity because he thought it was a way out of the poverty he had stumbled into, so he decides not to accept Jesus, and that night, he dies and goes to hell.
 * In G.I.Joe Vs. Transformers 2 the United States government decides to just nuke the heck out of the bad guys (who had all gathered on one island). Turns out nukes plus Energon, the highly-volatile substance that Transformers run on, equals Earthshattering Kaboom. Two heroes, Wheeljack and Mainframe and one villain, Doctor Mindbender, decide they want to live and stop the nukes by making a Kill Sat. Which then fries Mercer, a prominent good guy. Oops. The trio then has to break the Kill Sat, which fortunately doesn't cause any more innocent deaths.
 * Barry Allen decides that  So, he goes and chases Professor Zoom and stops him from   End result?  Oops.
 * He did this literally, on a smaller scale, in one issue of his original run. The Mirror Master falls in love with a woman trapped in a mirror, and tries to rescue her by tricking the Flash into taking her place. Barry realizes he's being sucked into the mirror--and shatters it, which traps her forever. Oops.
 * The Mighty Thor: In-universe, almost everyone considers Thor bringing back Loki (after he died in Siege) to be this. Loki was, however, brought back as a kid without any of his former emotional baggage (this was discovered to be one last shot at redemption/something like that by the original Loki). The trope's been subverted because so far the kid has one goal in mind: save Thor from the Serpent (and he if saves Earth too, then that's great!).
 * Plus, Thor insists that the real Nice Job Breaking It, Hero was how all of Asgard treated Loki as a villain because that's how it was written by the Norns, and therefore he became the villain they scorned him as. The main argument Thor has for keeping Loki alive is that with the Ragnarok cycle broken, even Loki has a chance to be good, and not have his fate predetermined.
 * Odin seems to be setting himself up for one, with the whole "raze earth to the ground to kill one enemy" thing. That won't come back and bite you in the butt ever. After all, the citizens of Marvel comics are so forgiving.
 * They're only unforgiving if you're a good guy. Bad guys says he's reformed? Let's put him in charge of S.H.I.E.L.D.! Nice job breaking it, Muggles.
 * Virtually the entirety of John Stewart's career consists of careening from one such moment to another. From getting his sister killed in a car accident to the destruction of two planets, John has pretty much the highest kill count possible while still being called a hero.
 * The recent Sonic the Hedgehog storyline had Dr. Eggman initiate Operation: Clean Sweep, a Cosmic Retcon that SHOULD have erased Sonic. Instead, it turned Mobius into its video game counterpart. Sonic turns Super Sonic and tries to reset things. However,, doing so futzes up reality, including