Biff is a catalyst. He drives Willy's actions and thoughts, particularly his memories, throughout the play. Whenever Willy is unable to accept the present, he retreats to the past, and Biff is usually there. Prior to his Boston trip, Biff adored Willy. He believed his father's stories and accepted his father's philosophy that a person will be successful, provided that he is "well-liked." Biff never questioned Willy, even when it was obvious that Willy was breaking the rules. As a result, Biff grew up believing that he was not bound by social rules or expectations because Willy did not have to abide by them, nor did Willy expect Biff to. It is not surprising that Biff's penchant for stealing continued throughout his adult life because Willy encouraged Biff's "little thefts" while he was growing up. For example, instead of disciplining Biff for stealing the football, Willy praised his initiative.
Biff's perception of Willy as the ideal father is destroyed after Biff's trip to Boston. Once he learns that Willy is having an affair, Biff rejects Willy and his philosophy. Biff considers Willy to be a "fake," and he no longer believes in, or goes along with, Willy's grand fantasies of success. Instead, Biff despises his father and everything he represents.
