Why is Willy Loman so desperate to portray himself as a successful salesman? --why can't he just admit that he's not a Dave Singleman?in Death of a Salesman
Considering Willy's pseudo-chauvinistic personality it would be very hard to imagine him adopting any behavior that is humble, nor passive.
Willy is a man on a mission. Even if his mission is misguided and founded merely on the few stories he has heard about Dave Singleman, it is nevertheless his goal in life to be like him.
However, the worst thing that happens with Willy is that he justifies his ambition by acting as if he were bigger, more successful, and more well-liked than what he really is. He feels as if she is "almost there" by acting as if he were already where Dave Singleman once was. This is why he talks down to people, encourages Biff to do as he pleases, takes in a mistress, and belittles his wife.
As we know, this is often the type of defense mechanism that people use to take control of situations. In Willy's case, he thought that by being petulant ,haughty, and a bully in general, he would be able to "act the part" of a successful man. Little did he know that, by doing this, he was less admired and less liked than ever.
Another thing is that the Lomans are a family with a tendency to deny reality. That, alone, is the key element that drives the lives of Willy, Biff, Happy, and Linda. They believe in whatever Willy tells them to believe. Each member of the Loman family enables one another. Willy creates the dream, and the family enable him by following his lead. Willy believes that he has the key rules to become a Dave Singleman; he believes that Biff will make it to college football; he thinks that being well-liked is everything; he feels that he "runs" some of the major sales areas of his firm. None of these things are true, but in Willy's imagination. As a result, these ideas rub off on his wife and sons. In the end, only Biff gets to realize that it was all a fantasy taken way too far.