Willy is a complex character. A man of great pride, Willy strives to realize a goal that is beyond his ability to reach. Willy's brother Ben stands as an example of the type of success that Willy has no chance to achieve.
Despite his limits, Willy is a person of some talent. He is a gifted carpenter and a hard worker. Despite these positive traits, Willy is also unfaithful to his wife. He is too weak to overcome his deficiencies and to weak to directly admit to his faults.
If his story is a tragedy, it becomes one because Willy:
...cannot face the reality that he has misdirected his energies and talents chasing a dream that never had any chance of materializing.
On a deep and fundamental level, Willy is delusional. He hallucinates and in this manifests conversations with this brother Ben. He is "twisting in the wind" of his own mind, unable to accept his flaws and unable to maintain a firm grip on reality. Willy seems to be driven to this mental state by the stress of age, job trouble and basic but deep-seated disappointment.
Though he has paid off his house and raised two childre, Willy fails to see any success in his life. His dream, so bright and impressive, overshadows the moderate successes he has actually achieved.