how this notion let Willy to think about his bad and good memories ? Explain elaborately with Examples ?

Willy is and unreliable protagonist so the flashbacks, seen through Willy's mind, become more interpretive for the reader. The audience cannot be sure if they are flashbacks, are accurate or merely a part of Willy's delusional flights of fancy. The past increasingly intrudes on the present in Willy’s mind and bolsters his feelings of guilt and self-recrimination over all of his failures including the affair he had.