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Happy might as well be Willy Jr., because this apple hasn't fallen far from the tree. Though he is relatively successful in his job, he has his dad's totally unrealistic self-confidence and his grand dreams about getting rich quick. Like Biff, but to a lesser extent, Happy has suffered from his father's expectations. Mostly, though, his father doesn't pay that much attention to him. Willy was always a bigger fan of Biff. Happy, maybe because he always felt second-best, has more of a desire to please his father. Despite his respectable accomplishments in business and the many, many notches on his bedpost, Happy is extremely lonely.
Happy is competitive and ambitious, but these feelings are misdirected. Unable to compete on his own terms in the business world, Happy blindly pursues women—like his friends' girlfriends—purely for the sake of doing so. Looks like he's taken his sense of competition to the realm of sex. Of course, this, much like the world of business, fails to satisfy him.
Most disturbing for Happy is the fact that he can't figure out why all this isn't working. He's followed the rules, done all the right things, yet Happy just isn't happy. His name highlights the irony of his predicament. If you consider the fact that parents name their children, you could say that Willy foolishly bestowed the nickname on his son in yet another display of misguidance and delusion. Nice.
Just as the saddest part of Willy's suicide is his continued delusion, the saddest part of Happy's ending is his own persistent misbelief. Still driven by what he feels he should want (money, a wife), he sticks to Willy’s foolish dreams to the bitter end.