In essence, Willy remains proud of his son's thievery and his attitudes toward it further encourage their acts.
Willy is a man who has striven from more than he achieved in life. He maintains that his sons are underachievers at various points in the play, but his attitudes toward their thefts are ones that further encourage them to steal rather than act with ethics. We see this in two other instances of theft. When he was younger Biff lost his job with Bill Oliver because he stole a crate of basketballs. We can see why he might have done so based on Willy's reactions to his theft of the football. However, Biff is becoming like Willy. He is beginning to believe in his own delusions about past events. Despite knowing he stole the basketballs from Bill Oliver, Biff still believes he will loan him thousands of dollars to start a ranch. However, when he goes to Oliver to ask for a loan for his new business venture, he cannot help but steal Oliver's fountain pen ruining any chances he might have had for the loan. In a twist of irony that shows Willy's actions and attitudes have influenced Biff's character, at Willy's funeral Biff maintains, "He has the wrong dreams. All, all wrong. He never knew who he was" (Miller 138). Ironically, Biff does not know who he is either and continues to maintain delusions about his past and present actions and character.
In conclusion, the motif of theft in Death of a Salesman is important because Willy creates a dishonest vision of those acts that not only encourages deviant behavior in his sons but also makes him and they convinced that their lies about these acts are the truth. This not only has the impact of placing Biff and Hap on a dangerous road in life because it encourages deviant behavior but it also, when Willy can no longer believe his lies are the truth, motivates him to commit suicide. When his longtime friend and neighbor Char