Answer: Polonius believes that the real reason for Hamlet's lunacy is his love for Ophelia.
Step-by-step explanation:
In Shakespeare's Hamlet, prince Hamlet decides to act as a mad man, so that he can revenge his father.
Polonius, however, believes that Hamlet has lost his mind because he loves his daughter, Ophelia, but she rejects his love. Polonius has told Ophelia that Hamlet is out of her league and ordered her not to be with him. Although she does have certain feelings for Hamlet, her father demanded that Ophelia ignores any love letters that he should send her. In Act II, Scene II, Polonius tells Claudius that this is the reason behind Hamlet's madness.