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.

The big thing that happened in high school is the fact that Biff did not graduate high school.  Biff was failing math in his senior year.  He had many opportunities to get tutored and improve his grade, but Biff was influenced by Willy's attitude.  This attitude was that Biff's athletic ability and good looks were going to guarantee Biff's success.  Biff has geared up to have a college scholarship, and Willy had filled his head with the idea that he (Biff) would go to college and be a great athlete and have much success.  Why worry about math?

So Biff doesn't worry about math - and then he finds out he is going to fail math, and therefore flunk out of high school and not have a chance to go to college and become a sucess.  Rather than accepting the consequence of his behavior, Biff rushes off to Boston to find Willy and to ask Willy to intervene with the teacher.  Willy's skewed sense of reality has affected Biff, who believes that sweet talking will get the job done.  However, he discovers his father's adultery in Boston, and loses interest in having his father speak for him.  Biff becomes disillusioned, and drifts on from this point, confused and unfocused.

This lack of hard work and this inability to accept the consequences of his action are exactly what are holding Biff back as an adult.  He is still looking for "the big idea", the "big plan" that will make him rich quick.  As a result, he jumps from job to job, gaining little wealth, little independence, and little happiness.  As an added detail to reinforce the lifetime of trying to get things quick, Biff was also a petty thief in high school - he steals things like footballs from the school, and thinks nothing of it.  He doesn't understand that this attitude is what is holding him back - and it continues to hold him back as an adult.  Even Willy finally shows Biff the truth of it, however, when he yells out, "“If you hadn’t flunked you’d’ve been set by now!”  Although Willy is still thinking about the sports and the "million-dollar" ideas, it is important that he places some of the blame on Biff - showing that Biff needs to accept consequences.