At the end of the play, Willy is deeply influenced by his son Biff to commit suicide. He loves Biff dearly and wants him to be financially successful in the way he himself has never been. Therefore, having no money, he gives Biff his life so that Biff can collect Willy's insurance money. (To be perfectly clear, Biff in no way wants his father to do this: this all comes out of Willy's ideas of the good life for his child.)
Normally, we think of people being influenced by older mentors, as Willy is by his brother and Dave Singleman, people who, at least in his fantasies, achieved financial success with ease and were able to sit back and watch the money roll in.
Willy wants to pass this idea of easy money onto his sons, especially football star Biff. Would Willy have followed his true, more modest vocation of gardening if he were not influenced by having sons to impress with a more flamboyant kind of financial success—a success he never can achieve?
Of course, Willy does nothing but destroy his sons' lives by trying to model for them a false idea of what success is. Even at the end, when he is influenced by his love for Biff to kill himself, it seems his values are in the wrong place. Again, it is all money that matters and money that he thinks will solve his son's problems, whereas they are probably beyond what money can buy.