Once he crosses that red line, there's no turning back.
"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. You are enemies of the universe... your Empire is doomed."
Named for the boundary around a 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
always be evil. That moment where you know for sure that it is simply not in their character to do something genuinely good and unselfish.
While they may not have had a term such as this to define it, many authors clearly recognized it.
Robert A. Heinlein's
Stranger in a Strange Land referred to it as being the result of an act that was "so bad, so black" that it was basically unforgivable. Hank Rearden in
Ayn Rand's
Atlas Shrugged said that "to convict a human being of that practice was a verdict of irrevocable damnation...
a 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 damnation.
Obviously, it follows from the definition that a character can't cross this boundary more than once.
note However, since this is YMMV, viewers/readers can have differing opinions of when a character crossed it — multiple viewpoints are permitted as long as it does not provoke an Edit War. Crossing it implies going from redeemable to irredeemable, and that's it; the other way around contradicts the definition. Note that this does not mean their morality is always decreasing after crossing this; a character can cross this, then become much more horrible than they were when they crossed it, then become just a little better than they were after that, but they will never, ever commit an act that redeems them entirely.
Sometimes all that stands between man and monster is a
Single Tear... or even a
full-out weep. Perhaps a show of respect for the enemy. A
Heel Realisation that you've gone too far is possible just as you're teetering on the edge of becoming a monstrosity - you've committed the act but you
regret it. Characters who regret the act that would otherwise make them cross the line effectively become
The Atoner. Just as with a real black hole, the closer you come to a
Moral Event Horizon, the harder you must try to escape. Sometimes a character who has crossed the horizon will invoke
I've Come Too Far afterwards.
Can lead to a
Complete Monster, but crossing the
Moral Event Horizon does
not automatically imply a
Complete Monster. The character can just be a bad person; the Moral Event Horizon is a black mark in their history that cannot be forgiven.
A character whom performs an act that should make them irredeemable but somehow gets away with it is a
Karma Houdini.
Compare with:
Contrast with:
- All Crimes Are Equal: When bad deeds are unforgivable, no matter how bad it is.
- Easily Forgiven: Sometimes, acts that really should be unforgivable are shrugged off in-universe.
- Felony Misdemeanor: When something that isn't really that big a deal is treated as utterly unforgivable.
- Adopt the Dog / Pet the Dog: An action by a morally neutral or ambiguous character that is meant to elicit audience sympathy for the character.
- Poke the Poodle: A half-assed attempt at villainy.
- Like a God to Me: Nearly the opposite of this trope. A character has done something so awesome that other characters fall over themselves to praise her/him.
Examples:
