''"I am writing a list of tragic character flaws on my dollar bills with a felt pen. I am thinking of the people in my universe and distilling for each of these people the one flaw in their character that will be their downfall—the flaw that will be their undoing. What I write are not sins;I write tragedies."''
— Tyler Johnson, Shampoo Planet
Heroes have a Fatal Flaw which they wrestle with on a consistent basis. This may open them up for specific conflicts later — when a protagonist's fatal flaw is encountered through the course of a plot, the audience's reaction is very tense.
This is not to be confused with what Aristotle calls hamartia, also a key part of Tragedy. A hamartia is a mistake or error a hero makes which leads to his undoing. It is NOT the same as a fatal flaw. This confusion arose from the misunderstanding of Aristotle' Poetics in the 19th Century.
In classic literature, a Fatal Flaw is often what prevents a Tragic Hero from succeeding, or serves as the cause of their Tragic Mistake. It is usually some sort of character deficiency listed below or, in conventional television, an addiction of some sort. In modern television, the Fatal Flaw is more likely to lead to a Very Special Episode.
Some specific Fatal Flaws:
Whether it be a raging inferiority complex, self-endangering recklessness, an Oedipus complex, alcoholism, bizarre neo-mystic delusions, or a complete disregard for one's own life, pretty much everybody in Neon Genesis Evangelion had at least one of these. Quite a few have more then one.
Light Yagami of Death Note has his overwhelming pride, which reaches A God Am I at its worst and blinds him to the point of refusing to even contemplate his own failure.
However, Suzaku is unable to see that the people he sucks up to due to his lack of self-worth and desperate desire to be a Britannian are everything that he does not want and he is doing everything he claims he is against on a daily basis.
Shirley's attraction to Lelouch gets her killed when she confronts Rolo. Even though, she doesn't remember him, she trusts him because Lelouch seems to trust him.
In Chrono Crusade, Chrono's demonic instincts and need to protect others (particularly Rosette) sometimes combine to give him a very, very dangerous temper. Since Chrono's powers drain Rosette's lifespan due to their contract, it's dangerous not just to him, but to Rosette herself. In fact, in the manga this trope is taken literally, when Aion provokes Chrono into unsealing his powers himself and come at him with everything he's got. Several people are killed in the battle, and it drains so much of Rosette's life that the next time she unseals the watch, she dies.
Death the Kid from Soul Eater has his raging OCD and self-esteem issues; the presence or lack of symmetry in his surroundings (or remembering that he may have forgotten to symmetrically fold his toilet paper roll this morning) can take him out of a battle in a heartbeat.
In one case, Liz actually uses this against him to avoid getting into a battle in the first place, as the factory containing the Clown scared her, (and with good reason). She does something similar earlier, when taking note of Free's ball and chain to provoke Kid to attack the werewolf.
The Salvage arc suggests that potentially each of the Great Old Ones has one of these which would make Beat Them By Compulsion a valid tactic against Physical Gods.
Yu-Gi-Oh! GX: Juudai's stubbornness, being headstrong, irresponsible, impulsive, and impatience are cute and endearing for two and a half seasons. Then all of those combine and (he thinks) gets four to five of his best friends killed.
From Durarara!!, Shizuo's severe anger issues and Kida's inability to face his guilt head on. Not only does this put him in a position where he avoids his girlfriend Saki they make up at the end of the anime series but by not facing this head on, he repeats his whole guilt trip with his best friend Mikado by dropping out of school and leaving Ikebukuro. And Mikado didn't take this well...
Tengen Toppa Gurren Lagann: Kamina's impatience, Simon's lack of faith in himself. (Of course, Simon beat his fatal flaw senseless about halfway along and went on to use its limp form as a club, but that's not important right now.)
Kittan's inferiority complex led to his Crowning Moment of Awesome when he stole a kamikaze attack Yoko was about to volunteer for.
The characters in Puella Magi Madoka Magica had their downfall brought by their respective Fatal Flaw. Sayaka's is Pride, Mami's is Loneliness, Madoka's is Selflessness, and Homura's is Ambition. And QB is thwarted thanks to his Lack of Emotion. Kyouko however, only died after she set aside her Selfishness. Death by Irony?
In Tiger & Bunny, Kotetsu has a noted tendency to keep personal struggles to himself, even when those personal issues don't just affect him. This starts really coming down hard on him in the second half of the series when he can't work up the nerve to tell Barnaby he's retiring, or the reasons behind it, and Barnaby takes it as a sign that he doesn't trust him.
And Barnaby has his own flaw; the hell-bent obsession with revenge that made him an Ineffectual Loner who has rejected any close personal relationships for the past 20 years.
According to Shura of Blue Exorcist, Yukio could be exploited by demons because he keeps his emotions bottled up unlike his more hot-headed brother Rin. Likewise, Rin has trouble controlling his flames because he's afraid of them.
Eri is a Clingy Jealous Girl. A hint of Harima getting paired with a girl sends her into a quiet rage which almost messed up her friendships with Mikoto and Tenma, and in the manga almost gets Tenma killed.
Future Trunks from Dragon Ball Z at first appears to have everything together: is a Bad Ass, has a tragic past, able to beat Freeza and King Cold like it was nothing. But as the arcs progress, his fatal flaw regarding his issues with Vegeta end up costing him big.
Vegeta himself allows his stubborn pride and arrogance to get the better of him several times.
Goku has one that rears its head on occassion: His love for a challenging battle. He projects this desire onto Gohan, who lacks said love, leading to Goku's death. Even after that, he still held back in his fight with Majin Vegeta so it would be more enjoyable, releasing Buu.
Most of the villains in fact have the fatal flaw of thinking there is no way they can be defeated. With Vegeta, it was a low-born defeating an elite. Freeza couldn't comprehend that a "monkey" could become stronger than him. Cell believes his final form is perfect (having the best qualities of each fighter) and thus cannot be defeated. Buu couldn't stand Vegetto's strength. All of them suffer a Villainous Breakdown when they are proved wrong.
In Bakuman。, Nanamine's fatal flaw is his inability to empathize with others. Not only does it lead him to twice attempt to rise to the top of Jump by using consultants, all the while viewing people as expendable, but it also means he is unable to write characters with "heart", in spite of his talent as an artist.
In the .hack fanfiction .hack//G.U.: The Staircase to Nowhere, each of the Epitaph users has one physical/mental flaw that can spell the end for them in the Goddess Morganna's war; Haseo has his photophobia (his sensitivity to light), Atoli's fear of being alone, Endrance's weak lungs, and Kuhn's color blindness.
Carlito's Way has a variation of this trope. Carlito's Fatal Flaw is either his determination to keep his "reformed" status, or his ties to his criminal past. If he had gotten rid of one of the two, there might have been a happy ending.
Actually, his fatal flaw was his belief that there was honor among thieves and street code you follow. It's how he went to prison in the first place, taking the wrap for the guy that would take over his territory. It's also how he ended up in a bad spot helping his best friend who turns out to be a snake. The scene when his girlfriend begs him not to help the lawyer is proof of that. Worst of all, he gets a good example and even admits there's no true friends among criminals, when his young relative gets killed in the beginning of the film. But you can't teach an old dog new tricks.
Jigsaw's MO is setting people up in traps (or as he calls them, tests and "games") where someone must overcome their Fatal Flaw or be destroyed. Seriously.
Nine times out of ten, they lose.
Full Metal Jacket's Sgt. Hartman's inability to deal with issues without using force.
Khan's obsession with taking his vengeance on Captain Kirk blinds him to some very bad mistakes and ultimately destroys him.
Kirk's hubris; his unshakable belief in his own ingenuity and command instincts. Therefore he's taken off guard by something that even raw cadet Saavik saw coming. And he arrogantly believes there's no such thing as a situation that he can't win. As his character develops throughout the film, he learns just how misguided he's been.
The Corleone Brothers all inherited a trait from their father (Sonny's charisma, Fredo's heart and Michael's cunning) which they don't have in each other. Had they worked together, they would have been unstoppable.
In The Hobbit, Thorin's biggest flaw is his pride, as lampshaded by Gandalf.
His grandfather Thrór became so greedy and obsessed in filling his halls with gold that it would attract Smaug and eventually led to the downfall of Erebor.
Daniel Plainview from There Will Be Blood thrives on animosity and he goes after enemies with a will. He ends up driving away the boy who he treated as his son and kills his arch-enemy without thought of consequence.
CLU in TRON: Legacy suffers from an unquenchable need for perfection. He inherited this from Kevin Flynn when he was programmed, but unlike Flynn he is a program and is unable to learn from his mistakes.
Hubris is a common tragic flaw in mythology and classical literature. One of the more famous examples is Odysseus, who is forced to undergo a 10-year voyage home after angering Poseidon with his arrogance.
In Percy Jackson and the Olympians, it's explicitly stated that every demigod has a Fatal Flaw which, if not mastered, will lead to their death. Annabeth's fatal flaw is explicitly stated to be hubris (except Percy thinks she says hummus). Percy's is personal loyalty—he will go out of his way to do anything necessary to save the people he cares about. Thalia's fatal flaw is that she has a weak resistance when she is offered power, to the point she seriously considered letting her friend down to become more powerful than the gods (though her conflicting feelings over this were apparent). It's a good thing Mr.D was able to step in otherwise she probably would have given in. Nico and Bianca have the Fatal Flaw of holding grudges, which they inherited from their father.
In the Backup Novella a "client" deliberately plays the part of damsel in distress complete with kidnapped child to get Harry's help as part of her plan, Thomas steps in without Harry knowing to save him.
His other fatal flaw is probably his temper. When he gets mad enough, he'll do almost everything in his power to destroy the bad guys with little regard for the consequences. He reevaluates this outlook in "Ghost Story", after the destruction of the Red Court throws the world into chaos.
Voldemort's Fatal Flaw is pride. It's not so much petty, plain-old narcissism and arrogance than it is outright full-blown megalomania. He's the smartest and most powerful wizard in the world and he knows it, so he tends to go out of his way to add a flair of grandeur and grace to his plans while attempting to achieve his objectives in the way he thinks will be more terrifying. For example, he challenges Harry to a duel in the graveyard sheerly for amusement, when the most pragmatic option would be to simply give the Avada Kedavra right there and then when Harry was tied up and couldn't escape. Thus, he doesn't realise that other people could learn about his Horcruxes, or find them, and he certainly doesn't realise that attempting to kill the boy destined to defeat you may result in that boy being actually able to defeat you. And thus, Harry Potter was given the weapons to destroy Voldemort.
Voldemort also cannot understand love, though he can't help that - he's The Sociopath whose complete incapability for love and compassion were caused by the fact that his mother coerced his father with love potion, which is not true love.
Voldemort is also so terrified of death — Word Of God states that Voldemort's boggart would look like his own corpse — that he doesn't believe that there could be anything worse. His quest to cheat death forever, combined with his other fatal flaws mentioned above, ultimately condemns him to a Fate Worse Than Death.
In another sense, Harry's fatal flaw is that he has a martyr complex that keeps him from asking for help or back-up at times when it would really be a smart idea. He does this to keep the people around him safe but it tends to really work against him. Voldemort uses this to manipulate him into events that lead to Sirius's death.
Severus Snape hangs on to the past to the point that he makes seemingly irrational choices simply because of some event or another that happened a long time ago.
When he was young, Dumbledore had a whopping case of Pride, planning to create a "new world" with Grindlewald in which wizards would rule over muggles. He snapped out of it with the death of his sister and spent more than a century deliberately avoiding powerful positions because he didn't trust himself (Headmaster of Hogwarts not being that powerful a job, apparently).
It's not that powerful a job. It's no more powerful than the principal of your high school, or the Dean of your university. In other words, lots of influence over the educational institution itself, but no power over you once you no longer attend.
Heathcliff of Wuthering Heights holds on to grudges and he spends his life getting even with people who were mean to him. He uses his own family as pawns and holds Kathy on such a high pedestal that he refuses to see that everything that happened to him was her fault. He is also blind him to the fact that his revenge can never last so when he dies and everything reverts back to normal, it's like nothing happened.
I don't think it's that he refuses to see that everything is Cathy's fault, (he gives quite a brutal "The Reason You Suck" Speech to her even as she's dying), so much as his obsession over her is so strong he can't break it even when he knows it's making things worse for everybody (including himself).
Ambrosio, titular character of The Monk, commits the sin of pride long before he starts committing any of his truly deplorable acts. It is his pride that allows him to believe himself holy while he continues to sin.
Book of Esther - Haman's conceit. He doesn't understand that he's just a despot's favorite and that he can be replaced at a whim.
Live Action TV
Homicide: Life on the Street - Frank Pembleton's self-righteousness and moral absolutism drive everyone away from him, and eventually force him to turn in Tim Bayliss, the closest thing he has to friend.
Breaking Bad - Walter White's pride causes him to start cooking meth instead of accepting charity in the first place, and continues to get him into escalating trouble from there.
Gus Fling's determination to get revenge against the men who killed his best friend is another major example. He even had a chance to avoid his death by letting his dragon kill the main object of his hate. But because he had to do it, personally, he walked right into a death trap.
House's vicodin addiction, irritability, and inability to have a healthy relationship.
In The John Larroquette Show, John Hemingway's (recovering) alcoholism.
Babylon 5 had Dr. Franklin addicted to "stims" for most of one season, and battling his addiction for a second; and Security Chief Garibaldi's alcoholism (which he had successfully battled for most of the show's run) formed a major part of the fifth season's arc.
Law & Order: Most characters from the franchise have one of these that occasionally clouds their ability to do their job ethically and fairly or discredits their testimony once in court. Briscoe had drinking problems, Logan was a hothead who'd occasionally rough up suspects, Curtis couldn't curb his infidelity, and so on.
The same with Law & Order:SVU. Olivia and her belief all women are victims when it comes to dealing with men, given that she was a product of rape. Fin and the revelation that he was a deadbeat father. Elliot and his marital problems at home.
Most of the cast of What Its Like Being Alone, including Armie, who only has one limb left, Aldous the Emo Teen, Princess Lucy, who would be the Alpha Bitch if she weren't fiendishly ugly, Sammie the alcoholic Fish Person, Charlie, who is always on fire, Seymour, who doesn't have a mouth, and other unfortunates. They're also all orphans.
Heroes: Pretty much every character on the show has a fatal flaw (drug addiction, insecurity, tendency to explode, carelessness.
Both brothers have no sense of self-worth thanks to Dad, who refuses to show any affection or let anyone help him, preferring to keep his sons completely in the dark. Not the greatest planner with vengeance on his mind, this works out badly.
Dean's self-loathing. His struggle to hold his broken family together, along with his sluttiness, death-wish, general bone-headedness, and feeling that he's only valuable as a "blunt instrument", all seem to stem from efforts to do enough that he feels worthwhile.
Sam's insecurity. His gullibility and pride seem to be born of his overriding desire to believe that bad people can be good—that he can be good.
Many of the characters in ER have one at some point or another. Examples include Abby's alcoholism, and Carter's painkiller addiction.
In Scrubs, the character Dr. Kevin Casey is an example of The Ace with a hidden Fatal Flaw. JD, Cox and Turk all despise him for being such an insufferable genius at everything he does. Until they see him suffering because of his obsessive-compulsive disorder, unable to stop washing his hands.
Nate's alcoholism in Leverage, which has gotten the team into trouble in at least one episode. Although, the way the new season looks, he might be on his way to beating that.
In The Chosen, Rebbe Saunders' near-fatal flaw was fear that his son would be unworthy. It is overcome because Danny loves his father enough to endure the harsh training that his father thinks he needs.
In the 1998 Merlin series, the titular character's fatal flaw is that he sees only the good in people, rather than their flaws, and thus expects too much of men. The villains also have their own fatal flaws, with Vortigern's being his Pride, and Uther's being Lust.
In The Vampire Diaries, Damon's impulsiveness, and Stefan's inability to control his addiction to human blood whenever he has even a little.
The Wire, most of the characters are flawed in their own way, but the most obvious example, would be Jimmy Mcnulty. Ironically, his whoring and drinking don't affect his work but rather his personal life to the point where he becomes a burden to those around him.
He can't be a good detective and a good person at the same time. Eventually, that leads to him doing wrong things in order to make the right case, which doesn't end well.
Wesley from Angel has a tendency to commit rash action usually for a good reason. It comes back to haunt him in seasons 3-4.
Shinya Arino of Retro Game Master/Gamecenter CX has major problems when it comes to certain gameplay twists, most notably when dealing with a Sequential Boss. Whenever he makes a major accomplishment, he starts cheering and lets go of the controller. The problem is that he plays games blind. Thus, he doesn't realize it's not over, yet he never seems to learn. It's been called "Heaven to Hell" on a few occassions. By the time he realizes what's going on, he's to shocked to rationally continue and dies. Sometimes he recovers and retries, sometimes he doesn't, most notably with Act Raiser.
Rumpelstiltskin is a coward. This leads him to become the most powerful magical entity in his world to make up for it and find his son.
August is really bad at resisting temptation. At the start of the series, he was off at some resort island using money he was supposed to send to Emma.
Regina is completelyGenre Blind and very emotional, which results in her being led around by the nose by Rumpelstiltskin.
Nikita is too secretive, stemming from her inability to trust.
Alex is naive and vengeful and is turned into Oversight's pawn.
In the system called House of the Blooded, the characters are all nobility, seemingly built for high drama and Mary/Marty Sue-ism. Each character has six characteristics, each based off of one of the major families, and there is no rolling involved. You have four points for one characteristic, three for two others, two for two more... and the sixth characteristic gets a zero, meaning you can never use it. A zero in Strength means you are too physically weak to force open a sticky door, for example, thus ensuring that all characters have an inbuilt Fatal Flaw that cannot be legally circumvented.
In Traveller the Fatal Flaw of the Vilani was in trying to call a halt to progress for the sake of stability. Which worked so long as they did not find an outside competitor(I.E. Earth) The Fatal Flaw of the Terrans was more complex. It was in trying to govern the thousands of conquered Vilani worlds without the experience or inclination. The Vilani system was too repressive for the Terrans to use it and the Terran system was only suited for governing a few dozen worlds.
The Solars, Lunars, Dragon-Blooded and Sidereals all get various versions of the Great Curse, a psychological affliction thrown at them by the Primordials for besting them in war. The Solars and Lunars enter a brief psychotic period called a Limit Break (ranging from berserker rage*
to uncontrolled crying at the suffering of the world*
Heart Of Tears.
to becoming cold and uncaring about the suffering of others*
The Abyssals, on the other hand, get Resonance. If, for some reason, they decide they don't want to go along with their masters' goals of feeding all Creation into the mouth of Oblivion and resume something approaching a mortal life, their Resonance will build until it erupts and risks destroying any emotional connections they've managed to make with the world of the living.
Even without supernatural curses or compulsions, each of the four virtues has drawbacks if you have three or more dots (and exalts have to have at least one virtue of 3+): compassionate characters have trouble making harsh decisions; temperate characters have trouble lying, cheating or going back on their word, no matter how dishonest the antagonist; valorous characters don't know how to back down from confrontation; and as for conviction, well... Oh and it's perfectly possible for a character to have 3+ in two or more virtues. If they conflict, tough luck!
The New World of Darkness also has the option during character creation of giving a character a flaw which could potentially hinder them and - if done right - give extra experience points. Some of the flaws include addictions, Coward, Forgetful, and Behavior Blind.
The Traitor Primarchs of Warhammer 40000. Other examples include the Emperor's failures as a father due to being too emotionally distant to treat them as much more than subordinates, or the Eldar's undying pride despite being on the brink of extinction.
Older Than Feudalism: Pretty much all ancient Greek tragedies had a main character or characters with a hamartia, which is often translated to English as "fatal flaw." It was part of the basic structure for an Ancient Greek tragedy, according to Aristotle. Oedipus was headstrong and didn't know when to stop, Creon in Antigone was proud and was intent on making an example out of Antigone, Antigone was stubbornly committed to her traitorous brother...
Shakespeare loves to give these to characters in his tragedies:
Brutus is extremely honorable and expects others to be, or possibly self-centered and susceptible to flattery.
Richard, Duke of Gloucester, a.k.a Richard III, has a callous disregard for human life and an irrational lust for the crown.
Hamlet waited too long, and is very likely crazy. And yet he is completely Genre Savvy about this: "So, oft it chances in particular men, That for some vicious mole of nature in them... Carrying, I say, the stamp of one defect, Being nature's livery, or fortune's star, Their virtues else ? be they as pure as grace, As infinite as man may undergo ? Shall in the general censure take corruption From that particular fault."
Romeo and Juliet are so obsessed with each other they forget about anything else. Romeo is a bit of a hothead, too.
Othello is too rash, not to mention gullible (to be more precise, he believes the people he shouldn't and doesn't believe the ones he should) and prone to jealousy.
KingLear is far to proud. This causes him to exile and disown his beloved, youngest daughter who tells him the truth and gets himself stabbed in the back by his two eldest daughters who tell him what he wants to hear.
Shown explicitly in Arthur Miller's play Death Of A Salesman. The main character, Willy Loman, is so entranced with his own dreams and desires, that he denies and ignores anything contrary to his beliefs. Willy's conviction that just being well liked is enough to lead to success eventually leads to his downfall, as he can't understand why his sons, who were popular in high school, can't seem to get successful jobs. After Willy commits suicide, the play ends as a Shaggy Dog Story, with nobody attending Willy's funeral. One of Willy's sons even Lampshades his father's Fatal Flaw.
Sweeney Todd: The Demon Barber of Fleet Street: Sweeney Todd's obsession with revenge against Judge Turpin (combined with waiting a little too long the first time he had him in his hands) ends up costing him everything in the end (as well as his willingness to trust someone he really shouldn't have concerning his wife's fate).
YMMV on the above. You could also argue that Sweeney's fatal flaw is naivety. "What was his crime?" "Foolishness". He failed to perceive exactly how dangerous Turpin was to his family, and all of the subsequent damage happened because of this. Case in point: it happens again. He's genuinely shocked by Mrs Lovett's betrayal - you get the feeling that even after his descent into total madness, he still can't comprehend the depths that some people will sink to.
In Electra, the title character's unrelenting lust for revenge combined with her nigh incestuous obsession with her brother, Orestes, and her father, Agamemnon, makes for her fatal flaw.
Though not fatal, Higgins' superior attitude causes Elisa to leave him.
Dungeon Keeper 2: Turned on its head in execution, but still used perfectly straight. One of the earlier campaign missions pits you against Lord Avaricious in his impenetrable fort. The elegant way to win (as opposed to a head-on slaughter) is to have your imps mine away almost all of the gold beneath his realm, enraging the man enough to lead the charge personally. It doesn't end well.
Eien no Aselia: Yuuto's fatal flaw in would be his stubbornness and anger. His life to this point has been more difficult than it needed to be due to the former, and because of the latter he nearly kills Kaori.
In Fate/stay night, Gilgamesh has a titanic ego and tendency to underestimate his opponents.
Shirou's need to save everyone constantly causes him problems and is what eventually led to him becoming Archer.
In The Sims Medieval, every Sim in your kingdom has some sort of fatal flaw that directly affects their mood or performance (ex.: Gluttons have to eat more frequently, and require more than one meal to be fully satisfied; Licentious Sims get in a bad mood if they don't kiss or Woohoo with other Sims after a set amount of time). Succeeding in certain quests allows them to drop their fatal flaw and replace it with a Legendary Trait, which can't be selected during character creation.
In Touhou, the Lunarians as a whole has a titanic ego and tendency to underestimate those they believe to be impure. To their credits, they are more powerful than most people in Gensokyo. Their arrogance eventually render them vulnerable to Yukari's plan... to steal Lunarian sake, Now that's just petty.
Reptile from Mortal Kombat is far too trusting and sides with any Big Bad on the promise that his people will survive. He dies in every game.
Happy Tree Friends: Almost all the characters have fatal flaws. Lumpy is inept at everything he does, Nutty is constantly hyperactive and addicted to sugar. Flaky has fears and phobias about just about anything and everything. These flaws do indeed prove to be fatal by the end of the episode. Sgt. Flippy's untreated post-traumatic stress disorder, always proves to be fatal for everyone else around him by the end of the episode.
Vaarsuvius has the fatal flaw of Pride in his/her magic power and intellect, which both leaves him/her wide open for the trauma factor of being completely powerless to stop horrible things from happening to his/her friends and loved ones and drives him/her to accept a Deal with the Devil rather than experience that feeling of helplessness again. Later he/she starts working on that, though, and is limiting him/herself to low-level enhancements unless he/she needs them, as opposed to just going all out.
Redcloak, whose inability to back down from the path and plan he's chosen, despite all the senseless sacrifices, really bites him in Start of Darkness.
Miko Miyazaki, a massive Knight Templar who refuses to believe that anything she does is wrong. Instead, she fabricates a massive plot behind the scenes just to thwart her. It's only when she's moments away from death that she starts to question something she does at all, but by then, it's way too late.
In Golden, a take-off of the standard fairy tale, the hero (and his less useful older siblings) are all sent off on the Quest because of their father's fatal flaw: GREED. The king wants gold very, very much. In fact, that whole family loves gold just a little too much to be healthy.
The Nostalgia Critic is trying to work on his temper and cynicism, but his insecurities about seemingly never being good enough are still getting in the way.
Danny Phantom: Danny has two: His darkness which manifests into him constantly abusing his powers which if he isn't careful, would result in a very, very, veryBad Future. The other is his emotions which he has a trouble time containing—the latter is often used to his advantage by some of his baddies. Unlike the first example, this is one he has yet to resolve.
Robin of Teen Titans tends to become so devoted to one goal, he neglects other aspects of his life until the issue is resolved. This characteristic has damaged, or even risked losing, many of his friendships and sometimes even proved his undoing.
While it is undeniably played for laughs most of the time, Omi, from Xiaolin Showdown has a massive superiority complex, constantly talks down to his friends as if they're beneath him, and it has gotten him in trouble more than a few times.
Also demonstrated with Raimundo. Due to being singled out of a promotion and treated as inferior by Omi, again, Raimundo betrayed the team.
In Avatar The Last Airbender, Iroh's bizarre Fatal Flaw is his love of tea. While normally the wisest and more sensible figure in the entire series, he makes some monumental mistakes when around the stuff. Once, when having to hide his identity as a Fire Bender, he used his bending to heat up some cold tea and nearly blew his cover. Earlier than that, when finding a plant whose leaves were either the world's most refreshing tea or pure poison, he ground it up and drank it due to temptation. It was poison.
Azula is another example. Her belief that people can be controlled through fear proved to be a mistake. Also Azula's determination to prove herself to her father, mainly because she believed that her mother only cared for Zuko, proved to be a serious issue that lead to a villainous breakdown at the end of the series.
Gargoyles have many examples. One of the strongest examples is Demona and her refusal to take responsibility and accountability for her actions. After all Demona was the reason why her Gargoyle clan was destroyed by the Vikings and why the surviving clan members got cursed, which is the genesis of the series.