The reader or audience knows something the character does not, and so the character's words and actions take on a meaning he himself does not perceive.
In The Brothers Karamazov
Set your minds at rest, I am not mad, I am merely a murderer!
The reader knows from Book XI that Ivan is telling the truth, and the room takes his words for delirium. The distance between what the reader knows and what the court understands gives each of Ivan's sentences a cruel weight.
Book XII: A judicial error, Ivan, in court, to the presiding judge