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[[caption-width-right:292:Once he crosses that red line, there's no turning back.]]
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->''"Tarkin, if ever there was a shred of humanity in you or these twisted creatures of yours, it's dead now. You're at war with life itself."''
-->-- '''Princess Leia Organa''', from the ''Radio/StarWarsRadioDramas'', after Grand Moff Tarkin wipes out her home planet.

Named for the boundary around a [[UsefulNotes/BlackHoles black hole]] from which there is no escape once crossed, this trope uses the black hole as a metaphor for evil; the Moral Event Horizon refers to the first evil deed to prove a particular character to be irredeemably evil.

Note the word ''irredeemably''. It is a demonstration of ''permanent'' evil; as in, the first evil deed whose role in the story is to tell us they will [[AlwaysChaoticEvil always be a bad person]]. That moment where you know for sure that it is simply not possible wash their hands to get rid of the damned spot of blood. And of course, many villains stay evil throughout, but we're talking "If you can find it in your soul to even consider forgiving this person, there's something freakishly wrong with you." Their existence is a blight on humanity. They poison the earth they tread upon. The very air they exhale is toxic fumes. [[PunctuatedForEmphasis They. Are. Vile.]]

While they may not have had a term such as this to define it, many authors clearly recognized it. Creator/RobertAHeinlein's ''Literature/StrangerInAStrangeLand'' referred to it as being the result of an act that was "so bad, so black" that it was basically unforgivable. Hank Rearden in Creator/AynRand's ''Literature/AtlasShrugged'' said that "to convict a human being of that practice was a verdict of irrevocable damnation... a [[CompleteMonster verdict of total evil]]" and that "he would not believe it of anyone, so long as the possibility of a doubt remained." Meanwhile, multiple religions have the concept of "perdition", where those who have committed a truly unpardonable sin are irrevocably doomed to punishment in the afterlife.

Obviously, it follows from the definition that a character can't cross this boundary more than once. Crossing it implies going from redeemable to irredeemable, and that's it; the other way around contradicts the definition. Of course, that doesn't mean they'll always be getting worse. Sometimes a character who has crossed the horizon will invoke IveComeTooFar afterwards... but they have still crossed the line. Yet there are ways to stem the descent into a true monstrosity. Sometimes all that stands between man and monster is a SingleTear... or even a [[TearsOfRemorse full-out weep]]. Perhaps a show of respect for the enemy. A HeelRealization that you've gone too far. Sometimes they become TheAtoner. But the act has been committed, and they will never fully succeed...

And since it's subjective, some characters will think you've crossed it, while others may be still prepared to believe in your possible redemption.

Just as with a real black hole, the closer you come to a Moral Event Horizon, the harder you must try to escape.

A CompleteMonster lives on the other side of the Moral Event Horizon, but crossing the Moral Event Horizon does ''not'' automatically imply that the crosser is a monster. The character can just be a bad person; the Moral Event Horizon is a black mark in their history that can never be forgiven. A character who performs an act that should make them irredeemable but somehow gets away with it is a KarmaHoudini. Unless [[HeelRealization they realize it]], [[MyGodWhatHaveIDone feel horrible]], and [[TheAtoner work their ass off to atone for that crossing]]. Then maybe it'll evolve into ForgivenButNotForgotten; that one crossing certainly will stay as a black mark, but they're working to be a better person. Such instances, however, are rare.

Sometimes, however, there is a positive usage of a MoralEventHorizon. If in a work, a villain seems to be too ineffectual and pathetic to be a threat, yet the show wants to insist that it's a dangerous villain, letting the villain cross the MoralEventHorizon can be a good way to establish that villain's caliber, that he's meant to be opposed. In other words, it can save a supposed villain from being a failure of a villain.

!!Compare with:
* AndThatsTerrible: When the writers [[ViewersAreMorons feel the need to explicitly point out when this occurs.]]
* CompleteMonster: A possible result. However, not all people who cross it become this (although if one's become this they've definitely crossed it).
* CopKiller: When a murderer demonstrates his lack of regard for morality by killing a representative of law and justice.
* CrossesTheLineTwice: When these actions are [[BlackComedy played for laughs]].
* DespairEventHorizon: A character who loses all hope can be likely to cross the Moral Event Horizon.
* DisproportionateRetribution: Sometimes, the retribution is disproportionate enough that it causes the person who committed it to cross the Moral Event Horizon, and [[HeWhoFightsMonsters often it does]].
* FaceHeelTurn: A good guy turns bad and allies with a villain (or group of villains) and forever affiliated with same.
* FauxAffablyEvil: Most AffablyEvil characters can become this when they cross the Moral Event Horizon.
* HeelFaceDoorSlam: A Heel-Face turn and/or an apology is ''attempted'', but for whatever reason(s) is rejected; in other words, it's too little, too late.
* HeWhoFightsMonsters: Where seeking revenge against the villains is a way of crossing the Moral Event Horizon, in that the character will turn out to be just as bad as them.
* IveComeTooFar: When a character recognizes (or believes) that he/she has crossed the MEH and knows that he/she doesn't have a chance of redemption anymore.
* JumpingOffTheSlipperySlope: A character skips over [[SlowlySlippingIntoEvil several progressively darker shades of gray]] and goes straight to the Moral Event Horizon.
* KarmicDeath: What the irredeemable character will usually face due to crossing the Moral Event Horizon.
* KickTheDog: An act which serves no purpose other than to mark the character as evil, which frequently overlaps with this.
* MyGodWhatHaveIDone: The character will react with remorse after he/she crosses the Moral Event Horizon.
* PaedoHunt: Sexual contact with a minor is treated as a Moral Event Horizon.
* RapeIsASpecialKindOfEvil: Rape is easily considered a Moral Event Horizon.
* RedemptionRejection: A character rejecting an offer to [[HeelFaceTurn redeem himself]] is proof that he isn't willing to turn back from the line he crossed.
* RejectedApology: Sometimes, a character's actions cross the line to the point where he isn't forgiven for them no matter how apologetic he is.
* SlaveryIsASpecialKindOfEvil: Slavery is considered a Moral Event Horizon. Of course this goes first and foremost for slavedrivers who start it and not for people who are raised in a slavery-based society if they aren't cruel to the slaves.
* SlowlySlippingIntoEvil: The approach to the Moral Event Horizon.
* ThisIsUnforgivable: An in-universe acknowledgment that the Moral Event Horizon has been crossed.
* TragicVillain: A character knows (or thinks) they've crossed the Moral Event Horizon, and has nothing left to do but continue to be evil.
* YouMonster: Characters will get called this, indicating that they've severely crossed the line.

!!Contrast with:
* AdoptTheDog / PetTheDog: An action by a morally neutral or ambiguous character that is meant to elicit audience sympathy for the character.
* AllCrimesAreEqual: When all bad deeds, whether big or small, are equally unforgivable, although the punisher [[HeWhoFightsMonsters may cross it if it is taken too far]].
* EasilyForgiven / InsaneForgiveness: Sometimes, acts that really should be unforgivable are shrugged off in-universe.
* EasyRoadToHell: Similar to AllCrimesAreEqual, except that all crimes automatically condemn those committing them to {{Hell}}.
* EvenEvilHasStandards: A villain isn't considered purely evil because he avoids crossing the Moral Event Horizon.
* EveryoneHasStandards: Even though they may disagree on where the line is, most people believe there are lines that shouldn't be crossed.
* FelonyMisdemeanor: When something that isn't really that big a deal is treated as utterly unforgivable, although the punisher [[HeWhoFightsMonsters may cross it if he takes it too far]].
* HeelFaceTurn: In which a villain turns good.
* HeroesFrontierStep: The good deed that shows a character will become a true hero.
* KickTheSonOfABitch: Unlike KickTheDog, where it's an act that marks a character as evil, this is where the act is forgivable because the one receiving it [[LaserGuidedKarma deserved it]].
* LikeAGodToMe: Nearly the opposite of this trope. A character has done something so ''awesome'' that other characters fall over themselves to praise her/him.
* PokeThePoodle: A half-assed attempt at villainy.
* ShootTheDog: When the hero crosses the line because [[IDidWhatIHadToDo it had]] [[NecessarilyEvil to be done]].

* MoralEventHorizon/AnimeAndManga
* MoralEventHorizon/ComicBooks
* MoralEventHorizon/FanWorks
* MoralEventHorizon/AnimatedFilm
* MoralEventHorizon/{{Film}}
* MoralEventHorizon/{{Literature}}
* MoralEventHorizon/LiveActionTV
* MoralEventHorizon/{{Music}}
* MoralEventHorizon/{{Religion}}
* MoralEventHorizon/{{Roleplay}}
* MoralEventHorizon/TabletopGames
* MoralEventHorizon/{{Theatre}}
* MoralEventHorizon/VideoGames
* MoralEventHorizon/WebAnimation
* MoralEventHorizon/WebComics
* MoralEventHorizon/WebOriginal
* MoralEventHorizon/WesternAnimation

[[folder:Newspaper Comics]]
* ''ComicStrip/{{Crankshaft}}''. The September 2013 plot arc has Crankshaft get even surlier than usual because a new co-worker is challenging his reign of smug, curmudgeonly idiot incompetence; his response is to try to 'scare' her into letting him be the festering asshole using his hard life as an excuse to be the antisocial clod he was born to be... by trying to run her over with his school bus.

[[folder:Professional Wrestling]]
* While deaths in the ring are not unheard of, they are extremely rare. So when Ox Baker killed Alberto Torres with his heart punch, that wasn't when he crossed the horizon. It was when he bragged about the death and tried to cause ''more'' with intentional heart punches that he crossed the line. And he was hated ''everywhere''.
* Wrestling/BigBossMan crossed it by killing AlSnow's dog and [[IAteWhat feeding it to him]], mocking the Big Show's father's death, and stealing his father's corpse at the funeral.
* Wrestling/ColtCabana crossed the event horizon in IWA Mid-South when he tried to rape Wrestling/ChrisHero's student, Nadia Nyce. In fact, some of his fans declare his IWA M-S run a DorkAge solely because of this incident or [[FanonDiscontinuity just choose to ignore]] that he was ever there.
* Wrestling/JimmyJacobs crossed the event horizon in the Independent Wrestling Association, or at least IWA Mid-south, when he appeared in rival promotion All American Wrestling and threw the IWA M-S Heavyweight Title belt in the trash. He's since shown up in IWA M-S again, in defiance of his permanent ban but is always the bad guy. He was considered a hero in AAW though, at least initially. He also crossed it in Wrestling/RingOfHonor when he tried to impale his ex-girlfriend the Lovely Lacey with a railroad spike, as even stablemates [[Wrestling/SethRollins Tyler Black]][[note]]though we've got more on him below[[/note]] and Joey Matthews felt he was going over the line.
* Wrestling/BrockLesnar either crossed it when he pushed an injured Zach Gowen down the stairs, or when he assaulted Wrestling/ShawnMichaels and broke his arm.
* Portia Perez crossed the event horizon when she tried to kill Allison Danger's unborn child. While she had {{masked|luchador}} baby{{face}} runs prior she was never really forgiven and retired in Wrestling/{{SHIMMER}} with no real friends, besides maybe Matthews.
* Wrestling/SethRollins crossed it when he took a retired Wrestling/{{Edge}} hostage and attempted to NeckSnap him even after Wrestling/JohnCena gave in to his demands.
* Johnathan Coachman crossed it when he punished Wrestling/JohnCena and his father, a non-wrestler, for double-teaming Wrestling/RandyOrton (despite it being in both self-defense and retaliation for Orton's own (repeated) aggression against the father) by making Cena watch his father get brutalized (again) in a match with Orton. Then, when Cena understandably attacked Coachman in grief and rage, Coachman tried to strip Cena of his title as further punishment, even mocking him for foolishly rendering his father's beating pointless (Part of the stipulation was that Cena would've been stripped anyway if his father had refused to wrestle.).