What happens is the opposite of what was expected, or of what someone planned, in a way that reveals something about the characters or the world of the work.
In Macbeth
We have scorched the snake, not killed it. [...] Better be with the dead, / Whom we, to gain our peace, have sent to peace, / Than on the torture of the mind to lie / In restless ecstasy.
Macbeth killed in search of security and now says that "better to be with the dead" than to live with the "torment of the mind." The king who has everything ends up envying the dead man he himself made.
Act III: The King Ruled by Fear, Macbeth
Yet here's a spot. [...] Out, damned spot! Out, I say! One, two. Why, then, 'tis time to do 't. Hell is murky. Fie, my lord, fie, a soldier, and afeard? What need we fear?
Act V: Sleepwalking, Birnam, and the Fall, Lady Macbeth
Let every soldier hew him down a bough / And bear 't before him. Thereby shall we shadow / The numbers of our host and make discovery / Err in report of us.
Act V: Sleepwalking, Birnam, and the Fall, Malcolm
I bear a charmèd life, which must not yield / To one of woman born. [...] Macduff was from his mother's womb / Untimely ripped. [...] Accursèd be that tongue that tells me so, / For it hath cowed my better part of man!
Act V: Sleepwalking, Birnam, and the Fall, Macbeth, then Macduff, then Macbeth
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