What happens to Biff during his visit to Bill Oliver?

Biff is locked in a cycle of deception and dysfunction in his life and his relationships with others, particularly his father. He has come back home after a failed attempt to live away from his father, mother, and brother. Despite his dislike of the city and office work, he allows his brother and father to talk him into seeing a former employer about a loan he can use to start a sporting goods business. In Act I the family, including Biff, imply that Biff formerly worked as a salesman for Bill Oliver. 

In Act II, Biff reveals he has spent the entire day in the reception room at Bill Oliver's office. After waiting six hours and even trying to flirt with the secretary to get an appointment, the man finally appeared at 5 p.m. Bill Oliver didn't even remember who Biff was, and he only spoke to him for about a minute. Biff found himself all alone in the waiting room. For some reason, he compulsively entered Oliver's office and stole his gold fountain pen. He realized he had never been a salesman for Oliver's company; he had merely been a shipping clerk. It dawned on him "what a ridiculous lie my whole life has been." After Biff stole the fountain pen, he ran out of the office and down eleven flights of stairs.

During the dinner at the restaurant with Hap and Willy, Biff tries to explain the situation, but Willy begins to lose touch with reality. Biff vacillates between making up a better story and telling the truth. He also reveals that in the past, presumably when he was employed by Oliver, he had stolen a box of balls from the company. Now having stolen from the man again, he can certainly never go back to speak to him about anything, let alone a loan of $10,000. Later he reveals that he "stole myself out of every good job since high school." However, stealing the fountain pen creates an epiphany for Biff. He looked at the pen and asked himself, "What am I doing in an office, making a contemptuous, begging fool of myself, when all I want is out there, waiting for me to say I know who I am!" Through this experience, Biff is finally able to look at himself and his life honestly.