The American Dream as a trap
Willy built his whole identity on the idea that charm and ambition lead to success. When that promise doesn't pay out, he has nothing left. The play shows how the Dream can become a prison when someone can't separate it from their self-worth.
Self-deception
Willy lies constantly, to his family and to himself. He inflates his sales numbers, rewrites his memories, and refuses to hear anything that contradicts his self-image. That self-deception is what makes him tragic rather than just unlucky.
Father-son conflict
The relationship between Willy and Biff drives the play. Willy needs Biff to succeed to prove his own life meant something. Biff needs to escape Willy's expectations to become himself. Those two needs can't coexist.
The gap between image and reality
Almost every character in the play performs a version of themselves that doesn't match who they actually are. Willy pretends to be successful. Happy pretends to be content. The play keeps pulling back the curtain on those performances.
The cost of false values
Willy taught his sons that being liked matters more than being honest or working hard. That lesson damaged both of them. The play traces how values passed down through a family can do lasting harm even when they come from love.