How is Willy affected by his good and bad memories?

In some ways, Willie doesn't have a present; he has present experiences, but it's so unpleasant that he lives almost entirely in the past.  I believe that this is one of Miller's themes:  the past does not exist in any real way, but its influence on the present is all pervasive, even if an individual's recollection is of a past that never existed.  Willie has both types of memories.  He remembers the days when he and Linda and the boys had an almost idyllic family life, when he came home and the boys were thrilled to see him, when they simonized (what an old word :)) the car each weekend, when Willie went out and earned a "living" for them.  Mixed in with these memories are recollections of salaries he never earned, of meetings with mayors that may or may not have happened, of promises that may or may not have been made.  And, of course, there is the horrible recollection of Boston and the buyer and Biff, memories that hang over his realtionship with Biff from that day on.  And there are the memories of Ben, memories of what might have "Been."  Who knows how true these are, but they clearly haunt Willie --- the dreams of what might have been.

All this reminds me of Frost's sigh at the end of "The Road Less Travelled."  We make decisions (salesman/explorer), and then see what happens.  For Willie, it wasn't all that great.