Joe Keller's guilt stems from a wartime decision he made to ship defective airplane parts, leading to the deaths of 21 pilots. This act of negligence, driven by a desire to protect his business and family, haunts him deeply. His guilt is a constant, oppressive weight that he attempts to suppress through denial and self-justification.
Keller's guilt manifests in several ways. First, it leads to a distorted view of reality, as he struggles to reconcile his actions with his desire to be a good man. Second, it fuels his anger and defensiveness, making it difficult for him to admit his wrongdoing. Finally, his guilt isolates him from others, as he struggles to connect with his family and friends. Keller's guilt is a central theme in the play, driving his actions and shaping his relationships with those around him.