The two traits that Biff acquired during his youth, but especially during his high school years, that kept him from success as an adult were dishonesty and an inflated sense of his own abilities. Toward the very end of the play, just a few pages before the Requiem, Biff faces...
The two traits that Biff acquired during his youth, but especially during his high school years, that kept him from success as an adult were dishonesty and an inflated sense of his own abilities. Toward the very end of the play, just a few pages before the Requiem, Biff faces the truth about himself and shares his revelations with Willy.
First, he says that the entire family "never told the truth" to each other. Evidence of that includes Willy's affair that he never confessed to Linda; Biff's unwillingness to tell Willy or anyone why he "gave up" on college; Hap's exaggeration about his job title; and Willy's lies about money and his job. Beyond that, Willy raised the boys to steal. They stole the lumber for their front stoop from a nearby construction site, and Biff admits that he "stole [himself] out of every good job since high school." Even while he was in school, apparently, he stole sporting balls. Eventually, Biff ended up in jail for three months for stealing a suit, and he steals Bill Oliver's pen when he tries to get a meeting with him. All of this deeply ingrained dishonesty interfered with Biff's success once he left high school.
Second, Biff tells Willy, "You blew me so full of hot air I could never stand taking orders from anybody." Willy made Biff feel as if he should not have to work as hard as others because Biff was a sports celebrity in his high school. Willy's preferential treatment of Biff—for example, above Bernard, the neighbor boy, or even Hap, Biff's own brother—went to Biff's head and made him cocky. Having to work at entry level jobs after high school came as a shock when he'd been practically idolized by Willy, Hap, and many of the kids at his high school. "Pride goes before a fall" is a maxim that proves true in the working world. Humility helps a person learn and grow, but Biff would just quit when he thought things weren't going his way.
At the end of the play, Biff looks honestly at himself with a realistic dose of humility, claiming, "I'm a dime a dozen." Although Willy and Hap refuse to give up their dishonest and untruthful ways, Biff chooses to change.