Willy devoted his entire life to Biff and when Biff does not succeed in life he blames himself for it. The main reason Willy blames himself for Biff's failure is seen by the viewers when Willy has a flashback in the story of when he was in Boston and Biff came to talk to him. He came to talk to him about talking to his teacher about his grade or attending summer school to make it up he caught him cheating on his mom. This was the beginning of the end for Biff and his respect for his father. Because of what happened with Biff's life and that Willy wanted to make it up to him he decided to kill himself so Biff could start over with the money he would get from the insurance. It is shown in the story how Biff, the person Willy most respected, once held him in a high position of respect then he lost it all.
A tragic flaw that leads to the downfall of Willy's character is his denial. Throughout the entire play Willy is in denial about everything that happens not only to him but to Biff as well. The biggest thing that Willy is in denial about is that he is a good salesman. The truth of the matter is that Willy has no business skills at all and is at best an average salesman. However, throughout his whole life Willy keeps telling himself that he is not only a great salesman but also the best on the east coast. Willy lies about how much he sells to everyone and lies so much that he actually begins to believe it himself. He is denial that he is not a good salesman and that he could have done something with his life that he was good at and that probably would have made him happier such as carpentry. He did not though because he views carpentry work as low and not of as great stature as being in business. Also, by lying to himself about being a good salesman and continually going on long business trips Willy loses the opportunity to be a good father and instill moral values in his children such as not to steal.