I have found
The very cause of Hamlet’s lunacy.

– William Shakespeare

Hamlet, Act 2, Scene 2. Polonius, who foolishly believes he is wise and all knowing, announces to King Claudius that he has discovered the cause of Hamlet’s madness – love for Ophelia. This is an example of dramatic irony, as Polonius is completely wrong about the Hamlet’s strange behavior, which stems from his father’s death and his mother’s hasty remarriage and also a certain amount of pretending to be mad.