The play is not really just about the Loman family, it is about the contrast of a family whose ideals are unrealistic compared with a family founded on hard work and realistic expectation.
Charley is used as a contrast to Willy. Willy constantly criticises and belittles his friend, and yet by the end of the play it is Charley who is providing Willy with an income. Willy always resents Charley and never seems to accept that Charley is quietly successful, while he is loudly unsuccessful.
Similarly, Bernard is a contrast to Biff and Happy. He is mocked as the gawkish teenager, even by Willy, despite his attempts to help Biff attain his dream of a place at the university of Virginia. It is through Bernard that Willy pinpoints Biff’s demise, after he discovers Willy has been unfaithful to Linda –
BERNARD:…I’ve often thought of how strange it was that I knew he’d given up his life.
Bernard is quietly successful like his father. He discusses how he is going off to do some work and play tennis, when Charley explains that Bernard is arguing a case at the Supreme Court. The brief but varied reactions in Willy show us how he is unable to understand the nature and origins of Bernard’s success –
WILLY [genuinely shocked, pained, and happy]: No! The Supreme Court!
Miller uses the successes of Charley and Bernard to magnify the failures of Willy, Happy and Biff.