Why has Bernard achieved the American Dream? What do Willy's mood swings mean?
Bernard achieved economic success. Although he was viewed as a "nerd" in high school, he studied, went through law school, and was on his way to argue a case before the Supreme Court when Willie runs into him in his Dad's office. Bernard was supposed to be a failure because he wasn't "well liked." This provides an antithesis to Willyh's argument that being "well liked" will get you far in the business world.
Willy's mood swings indicate that he is losing it. We know that he will commit suicide at the end of the play; his ever changing mood swings suggest at the mental instability that will lead him to make the decision that the best thing that he can do for his sons is commit suicide for the insurance money they will never receive.