What does theift represent? Especially in Biff.
In the play Death of a Salesman, by Arthur Miller, theft seems to be a tendency in Biff's behavior that is triggered when Biff feels that he is not in control of a situation. We know that not only Biff goes to jail for theft at one point in his life, but that theft is also the causative factor that gets Biff fired from every job he ever holds.
Biff's kleptomania has been evident from a very young age. Willy, however, never corrects Biff. This automatically turns a miscue into a full-fledged obsession.
Biff steals a carton of basketballs from Bill Oliver when he first works for him. He also steals a pen from Bill Oliver's desk when he is not recognized by the latter. He steals a football from his coach when he is a teenager (Willy gave him kudos for his "good initiative" in doing this petty crime). He is also encouraged by Willy to go steal lumber to show his uncle Ben how "fearless" he is.
In all, theft is a necessity in Biff's life only because it allows Biff to feel as if he has a hold on his own life. This, however, is also another bad behavior encouraged by Willy Loman during the years in which he is supposed to guide Biff towards a good and practical life.