Willy's dementia allows him to dwell not only on but also in better times that he is experiencing during the "present" moment of the play.
Happier times are recollected in this hallucinations and flashbacks, with Willy visiting with his successful brother Ben and basking in that success. Willy also re-lives the days of Biff's football success. In his dementia, Willy is sometimes buffered from his current travails and conflicts.
It is notable, however, that these flashbacks and hallucinations that define Willy's dementia also define the nature of Willy's failure. In his discussions with Ben, Willy's vision of success is articulated. At the same time, Willy's inability to achieve this particular (material and popular) success is also examined in these moments.