We remain immersed in the memories for whatever good, bad, pleasant, unpleasant happened to us. We wish whatever the good and pleasant happened to us, to be repeated again, and we curse on our luck for whatever the bad and unpleasant happened to us.
As for as good and pleasant memories are concerned, they are not going to be repeated in the same form because life does not repeat itself. So we should move on and let it go. We do not know what life holds for us. May be we could have more better and pleasant experiences in more exciting forms. And whatever bad and unpleasant has happened to us, we cannot eliminate that from our life. We could only minimize the effect of it by taking lessons from it doing good works right now.
Hence do not dwell in the past, it will only generate stress, fear and anxiety for you, and in turn it will make your present and future worse. Further do not stop enjoying your life in present movement. The good and pleasant experiences are spread throughout the life.