What does Laertes learn over the course of the play?
In Hamlet by William Shakespeare, Laertes is Ophelia's brother, whose passionate defense of his family leads to tragedy. During the play, Laertes endures the death of his father at Hamlet's hands, and the suicide of his sister, which he also blames on Hamlet despite her well-known insanity. To avenge his family, Laertes duels with Hamlet, and they are both killed by the treachery of a poisoned sword.
Despite his refusal to listen to reason, Laertes is a sympathetic character, and his familial losses are overshadowed by his desperate need for honorable revenge. When he at last learns the truth, and admits that King Claudius was behind the poisoned sword, he says:
He is justly served,
It is a poison tempered by himself.
Exchange forgiveness with me, noble Hamlet.
You are not guilty of my and my father's deaths.
And I am not guilty of yours.
(eNotes eText, Act 5 Scene 2, Modern)
Laertes realizes at the last that Claudius never cared about his honor and mission, and that he was used. Although he and Hamlet are dying, he seeks forgiveness for his blind rage, and forgives Hamlet in turn. His losses were personal to him, but simply a tool for Claudius to seek power.