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In Arthur Miller's Death of a Salesman, the irony I find in Willy's constant references to Ben's success is that Ben is dead. Whereas Willy has spent his working life believing he has missed the boat, regretting the fact that he never followed in his brother's footsteps, whatever Ben achieved in life, it is over. It is ironic that Willy continues to wish to be like his brother, when his brother has passed on. It is also interesting that Willy continues to talk with Ben and use him as a sounding board when trying to solve his problems. This is, of course, conversation that Willy imagines, made up of pieces of discussions from the past or imagined discussions. (There is no way to be certain.) This "relationship" that Willy has with his deceased brother supports the theme of appearance vs reality, and shows what a tenuous grip Willy has on reality throughout the play.
And for all that Willy sees life as a disappointment, he has two sons that can still make something of themselves, and a wife who loves him. It is ironic, also, that in hoping to be like his brother, Willy takes his life at the end of the play, following his brother to a state where success and failure are meaningless.