At the time of the play, Willy Loman is an aging salesman who wants more than anything to be respected, loved, and remembered for being successful. He has not done poorly in his profession; however, he has never been a top salesman. Rather than accepting his own personal talents and limitations, Willy blames his lack of success on factors other than himself. Early in the play, he complains that he has to travel too far to work and that this will hurt his sales. Because Willy does not accept himself, he has troubled relationships with others around him. Willy is critical of his sons Happy and Biff, and the boys resent him because Willy has never really accepted their dreams, preferring instead to try to live vicariously through his sons. Willy's wife Linda tries to be sympathetic to Willy's situation, yet he does not see or appreciate her efforts and is often sharp and terse with her. Willy is blinded by what he sees as the American Dream, and as a result, he cannot move past his illusion of what his life should be.
Willy's relationships are all failed. This is true largely because Willy seems incapable of dealing with reality. He does not engage with Biff as a person, but with Biff as an idea, as a bundle of potentialities. Though his relationship with Linda is better, it is still not good. He has cheated on her. He has been dishonest and continues to be dishonest. The lies he tells her are just another part of his pattern of behavior wherein we see Willy choosing to engage with fantasy instead of reality.
Perhaps Willy is best defined by his name itself. When we look at his mental characteristics, his physical characteristics, his employment record, and his relationships to others, he is certainly a "low man." His view of life and the world around him is certainly idealistic--some might say hopelessly idealistic--as it creates more problems for him than benefits.
Willy's job as a salesman identifies his own life. He tries to sell everyone, especially his family, on his own ideas and beliefs. When he sees his job slipping away, he also realizes he has lost control of his family as well.