Occurs when a situation turns out be the opposite of what you though it would be.
'The teacher's daughter is a high school drop out.' The chef won't eat his own cooking.' ' the barber always needs a haircut'. Bill Gates uses an Apple computer.
When the reader understands more about the events of a story than a character does. This is used to engage the audience and keep them actively involved in the storyline.
'Tim's parents are proud of the "A" he got on the test, but we know he cheated. 'Alex writes a love poem to judy but we know that Judy loves Kevin.