One of the primary themes of Death of a Salesman by Arthur Miller is the idea of illusion and reality. Every member of the Loman family spends time and energy clinging to illusions, primarily because facing reality would be too painful for them.
Willy is undoubtedly the worst offender and pays the highest price for it. He is a traveling salesman who believes many untrue things about his job, about people, and about life. He believes that success in life is based on how well people like him and how much money he makes. He claims to be a successful salesman, but all the evidence we have--most of it through his own mouth--suggests that he is a miserable failure at his job and has never been successful at it. He obviously still needs the money or he would not still be on the road at his age. The evidence is clear: he fails miserably on both counts, which is why he eventually takes his own life.
Almost as bad, Willy believes his sons are fine young men based on the same flawed standards. Once again he is pitifully deceived. He believes his boys learned proper behavior from him based on what he said to them, but in fact his sons learned their bad behaviors from him based on what they saw him do.
Even at the end of his life, Willy is not honest with himself. He commits suicide because he thinks his family will use the money will receive from his insurance policy to start a new business; we understand that this is never going to happen and is nothing but one final display of unreality.
Linda, Willly's wife, also lives a rather deluded life. For much of the play, we see her as the patient, loving wife who spends her married life making excuses for both her husband and her sons. She knows that Willy cheats on her, but she never admits it. She knows her sons are cheaters and failures, but you never hear her say so. The only reality she seems to face, at least in part, is that Willy intends to commit suicide. Even then, she does not do enough to stop it, and that is another escape from reality.
Happy has spent his entire life trying to please his father, but of course that was an impossible goal. Happy has also become a cheat and a liar, and he has tried to convince himself of the lie that he is successful. He spends his time and competitive energy on chasing women that belong to other men, deluding himself that he has achieved something fantastic in doing so. Ironically, Happy's greatest escape from reality is that he thinks he is happy. Of course he is anything but that, and by the end of the play we see no indication that anything in his life is going to change. His illusion will outlive his father's.
Biff is the only character who does seem to recognize that he is living a deluded life, but of course he is virtually powerless to change things at this stage in his life. He steals, he cheats, and he never lives up to his potential because he spends his life believing lies about himself and others. Eventually he faces the truth, and it is devastating.
How the hell did I ever get the idea I was a salesman there? I even believed myself that I’d been a salesman for him! And then he gave me one look and—I realized what a ridiculous lie my whole life has been. We’ve been talking in a dream for fifteen years. I was a shipping clerk.
When Biff finally forces his father to see the truth, Willy is crushed and loses his will to live.
This family suffers because it cannot face reality; however, I wonder if they would have been strong enough to face their truths.