Willy Loman has a very difficult relationship with his sons. His relationship with Biff is especially fraught. This is because Biff hasn't achieved his potential. Once upon a time, Biff was a star football player in high school and seemed destined for success. A well-liked man with a large circle of friends, he seemed to have it all. But after he caught his old man having an affair with a secretary, he went completely off the rails, so much so that he flunked his math test, thus missing out on a college scholarship.
Ever since then, Biff has been nothing but a disappointment to his father, even though it is Willy himself who's largely responsible for his son's failures in life. As for Biff, he cannot respect Willy, not just because of the incident with the secretary, but also because Willy has become a dinosaur, unable to change with the times when it comes to the modern world of salesmanship.
Happy is also a disappointment to his father. Although he has a better relationship with Willy...
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