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 Dom Casmurro
"You Will Be Happy, Bentinho!"
The voice that promises Bentinho happiness precedes a marriage that ends in separation, and the narrator, comparing the voice to the witches of Macbeth, whose prophecy leads to ruin, is the one who sets the promise beside an outcome the reader only learns later.
I did not say it so that you would not suspect
Chapters CI to CXII: The Marriage, the Sea, and the Son, Capitu
Subscription
The explanation of each passage, in every device and in every work, comes with a subscription.