A Tragedy of Impulsiveness

"The Council was divided. Mine was the deciding vote. They killed him. I was furious. I never knew myself capable of such rage. All I could see was death."

—Delenn, Babylon 5

A Tragedy Of Impulsiveness is when a tragedy is caused by someone's impetuousness or irrational impatience. This trope's power comes from the fact that if characters had thought before they acted the tragedy could have been avoided.

From seeing enemies where there are none, to jumping in a swimming pool before checking for water, to messing with the Mad Scientist's machines, acting without considering consequences can cause catastrophic calamities.

This is most likely to be caused by Leeroy Jenkins, or any Hot-Blooded character in general.

Examples of A Tragedy of Impulsiveness include:

Anime and Manga

Ai no Kusabi: Green-Eyed Monster Guy has decided to "rescue" Riki, his former lover, from Iason by first drugging and cutting off Riki's penis to remove the Pet Ring. Then by proceeding with a plan to Murder the Hypotenuse by blowing up a fortress. He failed to consider a couple of key things. First off is the fact that Iason is a Blondie and therefor, bigger, faster and stronger than he is and won't be happy when he learns what Guy has done to Riki. When he faces off with Iason, it's an inevitable Curb Stomp Battle so Guy then tries Taking You with Me by setting off his explosives. Second, he never considered what Riki thinks of this plan who has come into the building to stop him because he never agreed to it. End result; Iason and Riki die while Guy survives to think about what just happened that got his beloved killed.

Film

In Scarface, Tony's aggressiveness certainly didn't win him any allies, but you know he's doomed when he kills Sosa's henchman. It was for a good reason, but if he'd thought out his actions he could have avoided the situation without antagonizing the only person who could have fixed the mess he was in. Then later, instead of trying to fix the situation, he kills his best friend in a fit of rage, driving his own sister to try to kill him.
- The latter part was mainly motivated by a combination of his (rather messed up) protectiveness toward his sister and his increasing instability due to breaking a rather key rule of the drug trade in the movie (that rule being "don't get high on your own supply.").
Similar to the Romeo and Juliet example below, in West Side Story, Tony tries to stop a fight, but Bernardo kills Tony's best friend Riff, and an enraged Tony kills Bernardo (his girlfriend's brother).
Carlito's Way might count. Carlito himself is pretty level-headed, but his lawyer friend Kleinfeld dooms the entire cast by impulsively killing his mob boss client during a jailbreak.
Played for laughs in The Naked Gun, where Drebin shoots five actors ("Good ones!"), because he thought that they were killing a guy. It was just a production of Julius Caesar.
The entirety of Bad Lieutenant Port of Call New Orleans is this, especially at the beginning, where the protagonist jumps in water to save a prisoner without checking how deep it is, thus screwing up his back, getting him promoted and addicted to cocaine.
Alpha Dog is a good example. A gang of drug dealers has a grudge against Jake, who owes their leader money. While driving down the street, they notice Jake's little brother walking alongside the road. Without stopping to think of the consequences, they kidnap him in order to teach his brother a lesson. They eventually realize what dire consequences, namely hard time, their actions could actually have, so they kill the boy. A tragic ending that could have been avoided had one person actually stopped to think "Hey wait, kidnapping a 15 year old kid might get us into some trouble!".
- Even afterward, Jake preferred hanging out with his kidnappers to going home. He liked the gang and was perfectly willing to tell the police that he'd run away. If they'd just let him go, they probably would have walked away free. Instead everyone involved wound up in prison for kidnapping and murder.

Literature

Probably the ur-example: The Iliad (Paris stealing Helen, Achilles and Agamemnon fighting over Briseis, etc.).
- The Odyssey has some examples, too (like most of the sailors' deaths), but it isn't really a tragedy.
- And of course The Aeneid, which is sort of a Roman crossover fanfiction to the other two, has its fair share as well.)
Zakath's backstory in The Malloreon involves him having his fiancee executed and discovering afterwards that she was not part of the conspiracy to kill him.
Harry Potter and the Order of the Phoenix. Harry had been told many times not to trust his visions, and then completely forgets that Snape had means to contact Sirius. If he had gone to Snape before attempting to contact Sirius himself (and getting caught by Umbridge in the process), the whole misunderstanding/deception that led to Sirius's death probably would have been prevented.
The book The Fuck-Up is about a guy doing one of these things after the other, starting small and gradually escalating Up to Eleven until his whole life is a horrible mess. The Freudian Excuse is that his girlfriend broke up with him in the beginning of the book and it upset him so much that it made him act stupid, then all the mess that ensued continued to make him more emotional and stupid.
One of Dale Brown's novels touches briefly on an in-universe aversion; apparently the US Air Force has quite an extensive background certification process for pilots wishing to take a posting where they may be called upon to deploy nuclear weapons (which seemed to happen at least once in every volume at one point in the series), which is temporarily suspended in the event of personal crises like getting divorced. Brown being a former Air Force pilot himself, and the absence of any large and faintly glowing craters where US towns and cities used to be, suggest that this is Truth in Television.
In Native Son, Bigger Thomas accidentally kills Mary Dalton by suffocating her with a pillow while trying to prevent her from being observed in the same room as him. He feels no remorse for her death, but realizes that if he is caught he is likely to be sentenced to death for not only murder but rape. He unsuccessfully attempts to avoid this fate with increasing desperation and impulsiveness.

Live Action TV

The Wire. In season 2, Ziggy Sobotka loses his temper after being insulted one time too many by Glekas and shoots Glekas to death and wounds a stock boy. Ziggy immediately regrets the decision and confesses to the crime. His actions further result in The Greeks cleaning out Glekas's store before the detail can raid it, and Ziggy's peril is used as leverage to buy Frank's silence, which ends in Frank's death.
Delenn in Babylon 5, "Atonement" and "In the Beginning" starts a war with the humans in a spurt of grief and rage and spends years trying to make up for it.
Marian's death on Robin Hood is caused when she puts herself between King Richard and Guy of Gisborne's sword. This in itself is not the deciding action, but when she impulsively (and unnecessarily) tells Guy that she "would rather die than marry you!" and that she's in love with Robin Hood.
Narrowly averted with Vala in Stargate SG-1. When battling the dragon (It Makes Sense in Context), Daniel figures out that the key to victory is to speak the name of the person who set up the whole quest in the first place: Morgan Le Fay. Vala then charges out into the middle of an open field to confront the beast while shouting "Morgan Le Fay!" not realizing that they need to use Morgan's name in Ancient, Ganos Lal. It is only Daniel's quick thinking that saves her.

Music

You Lost My Memory by Skyclad ("...because of mere trivia misunderstood").

Myth And Legend

Extremely common in Greek mythology in general, though, so who knows what the actual Ur Example is...
- Pandora's Box, proof that curiosity killed the Classical utopia.
- Persephone's six pomegranate seeds.
- Hera deliberately invokes this, causing an Unstoppable Rage to fall upon Heracles (who was already a guy infamous for his temper tantrums).
- Arachne and her poorly-thought-through tapestry subject.
- Orpheus getting too excited and looking back before his beloved made it out the underworld.
Adam and Eve and the forbidden fruit.

Theatre

In Romeo and Juliet, Romeo's friend Mercutio fights Juliet's cousin Tybalt for Romeo's honor, and dies before Romeo can stop the fight. An enraged Romeo immediately kills Tybalt. More drama ensues... When Romeo uncovers Paris as an innocuous rival to Juliet's affections, Romeo, with no provocation, kills Paris, and then kills himself, causing Juliet to kill herself.
In Othello, the title character, with only circumstantial evidence and testimony from a Manipulative Bastard False Friend, believes that his wife, Desdemona, is cheating on him. He proceeds to have Cassio, her supposed lover, killed, and ultimately kills Desdemona himself. When the truth is revealed, it drives him to suicide.
In Hamlet, the eponymous main character, after blowing his first chance to kill Claudius, strikes out blindly when he thinks he has Claudius again, only for it to turn out that he's actually killed Polonius, the father of the woman he loves, which sends everything straight to hell for him.
- A common joke amongst Shakespeare buffs is that had the impulsive, quick-to-anger Othello and the ponderous, witty Hamlet been placed in each others' plays all of the problems would have been solved by the end of the first act and nothing would have gone wrong at all. Sort of negates the point of tragedy, though.
The later acts of Twelfth Night threaten to turn into this. Sir Toby and Fabian bait on Sir Andrew to attack "Cesario" on sight. This backfires on them when they meet up with Cesario's identical twin brother, Sebastian, who, unlike Cesario, is a good fighter. Anthony, who loves Sebastian, enters the fray, which gets him into trouble with the local Duke, who is the real Cesario's employer. And the Duke loses his temper when he finds out that his beloved, Olivia, has married Cesario. This being a comedy, however, things work out all right.
Oedipus Rex killed his father for basically cutting him off in traffic. He married his mother completing the other half of the famous complex at leisure though.
The Lieutenant of Inishmore—because when you tell Mad Padraic that his cat is doin' poorly, and it turns out to be Blatant Lies, he's not going to listen to reason, he's not going to be kind to that other cat you picked up, and in fact the only thing stopping him from killing the men he holds responsible is three more men with guns barging in on the little house.
Le Cid (adapted from the same story El Cid is) may be the poster child for this. Two old military officers have an argument that degenerate so much that Don Sanche wants a duel to death with the Count. As he is too old for this, he puts his son in charge of this. And he does. Seriously, couldn't the Count try to arrange things with Don Sanche rather than duel to death with his daughter's fiancé, which means whatever the outcome of the duel is, her heart will be broken?
In Much Ado About Nothing, several characters invoke this trope by making Claudio believe Hero died of grief after he jilted her. She's actually quite alive.

Video Games

Implied to be the case with the Axe Ending in Nine Hours Nine Persons Nine Doors: Clover works out a plausible but completely wrong solution to who killed her brother and acts on said misconception, killing both suspected murderers and the protagonist's Love Interest before turning on the protagonist himself. Averted in the True Ending, where the protagonist befriends her and inadvertently stumbles across a crucial clue that indicates her brother is still alive.
Usually in Sengoku Rance, Rance's instincts are spot on, and doing the first thing that leaps to mind works out pretty well for him. The exceptions are generally anything involving Miki, the Demon King, such as when she suggests he try to shatter the ice holding his slave, Sil. If you let him follow her advice, Sil dies.