In "Death of a Salesman," why did Willy think it was ok for his son, Biff, to steal the balls?
Biff was Willy's "golden boy" and his hope to see great success. For a while, Willy lived vicariously through Biff when he was successful at playing football.
Willy favored Biff to Happy in many ways be the way he treated him. Willy wanted Biff to go on to play football for a career and to be the shining success that Willy never truly became. However, Biff never lived up to that. He turned out to be a failure in more ways than one! However, Willy still made excuses for Biff's bad behavior; whereas, he tended to "lay into" Happy when he made poor choices and mistakes. Happy sees this and senses this, and it makes Happy resentful.
Biff finally realizes after his father's death that Willy had the wrong type of dreams and aspirations. eNotes states:
In the Requiem scene at the play's end, Biff illustrates that he has truly come to an understanding of his father's failure to achieve success, observing that Willy "never knew who he was" and that he "had the wrong dreams."
One of the characteristics that makes Willy Loman a classically tragic figure is his consistent state of denial. He is in denial about so many things; his failure as a salesman, the unhappiness of his family, his own weaknesses. His unwillingness to see Biff's criminal behavior for what it is, is a part of that denial and helps to bolster Arthur Miller's theme of the degradation of American society due to the relentless pressure on the middle class to succeed.