Biff's problem lies in the fact that, even though he does not want to associate with Willy, he cannot change the fact that he is his son. And as a result, he cannot change the fact that his father has inevitably affected him. It is true that Biff is not a womanizer like his brother Happy, but he has incorporated Willy's tendency to exaggerate and manipulate reality in his favor. For example, Biff truly believes he was a salesman for Oliver, rather than a shipping clerk. It is only when he confronts Oliver that Biff realizes how wrong he was.
Biff is different from Willy because he does finally accept and embrace the fact that he has been living a lie all of his life. Biff is relieved once he realizes who he is and what he wants, as opposed to who Willy thinks he should be and who Biff needs to pretend to be in order to please him. Once Biff states that "We never told the truth for ten minutes in this house," he severs himself from Willy because he openly refuses to live by Willy's philosophy any longer. Ironically, Biff reconciles with Willy almost immediately following this statement. Since he acknowledges that he, too, is a "fake," Biff can no longer hold a grudge against Willy.
