Willy Loman is convinced that success is a product of hard work. While this can be true, the vicissitudes of life mean that hard work may simply mean hard work, with no ultimate payoff at the end. He bases most of his philosophy off the successes of his brother Ben, who worked hard but in a different venue; Ben prospected in Africa and struck it rich. Willy, however, doesn't understand the role that luck played in Ben's success, and believed for his whole life that he could get ahead in sales through sheer persistence. Instead, he runs as fast as he can just to stay in one place, and never achieves his dreams.
WILLY: Don’t say? Tell you a secret, boys. Don’t breathe it to a soul. Someday I’ll have my own business, and I’ll never have to leave home any more.
HAPPY: Like Uncle Charley, heh?
WILLY: Bigger than Uncle Charley! Because Charley is not liked. He’s liked, but he’s not -- well liked.
(Miller, Death of a Salesman, Google Books)
Willy's single-minded pursuit of success overpowers everything in his life, shielding him from the advice and love of his family. He is unable to see past his dream, but refuses to take risks or change his situations to achieve it. Instead, his mind is warped with envy and anger, and he never truly realizes that his dreams of success should have been focused on his own happiness, and more importantly, that of his family.