After Willy's suicide, Biff does not view his father as a coward, but as more of a tragic hero. He has come to understand how his father's mistaken dreams and ideals led to all his (Willy's) disappointments. By clinging to a romanticized version of the American Dream, all dressed up in material success and popularity, Willy set himself up for failure. That is why Biff vows to take himself away, out west, to work for little wages and no recognition at a job he loves. Happy, however, having not learned what Biff has learned, misinterprets his father's suicide as a result of society's pressures, and vows to take up Willy's dreams and see them through.
