The confrontation between Biff and Willy toward the end of the second act brings the conflict between father and son to a point of full articulation. Biff has realized his own failings and realized largely where those failings began.
Confronting his father about the rubber hose and the false dreams that sustain his illusion of self-importance, Biff gives voice to the important lesson he has learned through the action of the play.
Biff expresses his rage over the “hot air” and phoniness that made him a dissatisfied, fake person.
Before this confrontation, Biff has begun to see who he really is and has begun to see where he started to "go wrong" with his life.
With the flashback to the scene in Boston where Biff catches Willy with a woman in a hotel room, the audience and Biff identify Willy as a cheat, a fraud, and as a man defined more by weakness than strength. Though Willy has tried to be a good person, his weaknesses win out over his virtues.
Biff's failed attempt to get a loan coupled with the flashback serves to demonstrate the similarity between Biff and Willy. They are both apt to believe in a false dream instead of facing reality. They prefer bluster over substance. For Biff, however, this aptitude finds its end in the argument with his father.
Initially, Biff is willing to take blame for his own failings and even allow Willy to escape any share in that blame. He tells father, “This isn’t your fault; it’s me, I’m a bum.”
Willy quickly seizes what he sees as an advantage and attempts to take a moral "high ground", trying one last time to win his son's respect through an outpouring of bluster and bad advice.
Biff's outraged response comes in part because he has finally seen himself clearly and without pretense. He has thrown away his excuses and accepted the notion that he has failed in life for a number of reasons; one of those being that he chose to believe he was better than he really is.
This hard-won humility makes no impression on Willy, yet this is a very important moment in the play. This is, ultimately, the great difference between Biff and Willy.
Biff understands that Willy is close to giving in and committing suicide. He also seems to understand that this state of mind has been brought on by Willy's persistent delusions of grandeur.
Willy is not as good as he wants to be. He is not as good as he says he is. He is a fraud. Biff, in this emotional climax of the play, attempts to show Willy that one can live without delusions.
“Pop, I’m nothing! I’m nothing, Pop. Can’t you understand that? There’s no spite in it any more. I’m just what I am, that’s all…. Will you let me go, for Christ’s sake? Will you take that phony dream and burn it before something happens?”