Biff Loman is Willy Loman's eldest son in Arthur Miller's play Death of a Salesman. After much realization and thinking, he comes to the conclusion that his life has been nothing but a byproduct of Willy Loman's personal dreams. That his father's eternal quest for his own idea of the American Dream has somehow trespassed into Biff's own psyche, making Biff almost make the same mistakes as Willy has.
This is not a simple thing to admit. Biff has lived his entire life under the ideas that Willy has put in his head. It is not until Act II when he finally confronts himself, and Willy, about it.
BIFF: (Crying, broken) Will you let me go, for Christ’s sake? Will youtake that phony dream and burn it before something happens?
Biff knows that his father as well as his grandfather and even himself are men who enjoy working outdoors, with wood, and with freedom.
BIFF: [...] Mom, I don’t fit in business. But I’ll try, and I’ll make good.
HAPPY: Sure you will. The trouble with you in business was you never tried to please people.
BIFF: I don’t care what they think! They’ve laughed at Dad for years,and you know why? Because we don’t belong in this nuthouse of a city!We should be mixing cement on some open plain or — or carpenters. Acarpenter is allowed to whistle!
Willy attests to that much, but rejects this by downplaying it as if it were a bad thing to work in some kind of trade work.
WILLY: Go back to the West! Be a carpenter, a cowboy, enjoy yourself!
Therefore, when Biff says that Willy has the wrong dreams all along he basically expressed how his father never takes the time to explore what he is good at and essentially goes after the success dreams of other men who do make it rich.
However, Willy is really never successful. He only succeeds at dreaming and at hoping. Since he is not living up to his best talent, he cannot give 100% at anything. Even Linda admits it:
Willy Loman never made a lot of money. He’s not the finest character that ever lived. But he’s ahuman being.
Therefore, Willy's chasing of other people's dreams ultimately renders him as a man that has nothing to give and very little to leave behind.