In Arthur Miller's Death of a Salesman, main character Willy Loman is a salesman whose main problem is his tendency to fantasize and believe his own fantasies.
The first fantasy that he believes is that he is a successful and well-liked salesman who has achieved the American Dream. The second fantasy that he believes is that his two sons, particularly his eldest son, Biff, are equally successful and well-liked.
Biff is Willy's favorite child not only because he is the first-born, but because since early in his childhood he demonstrates great abilities in football. For this reason, Willy basically banks on Biff as his successful heir and truly believes that his triumphs in football will take him very far.
We know that Biff fails Math and, for that reason, is not able to enter college. Furthermore, he discovers right there and then that Willy is having an affair. Willy knows that he failed Biff in many ways, but continues to deny everything and insists on living in his fantasy world. Therefore, it is his hope, and not his real dealings with Biff, what makes Willy embellish who Biff really is.