Every loss teaches us something, so I try not to forget at all.
That must be a large brain retention ability, all my losses in gambling is way too much to be able to think about them all, only new gamblers can do this, there are some losses that I can forget because of the circumstance around them and some were the events of the game, but a usual gambler can not keep all of their losses in their head. I just try to forget my loss and a win helps me do that.
Big losses or close wins could be painful. When you lose an amount you cannot afford to lose, it could be retained in your memory for a long time. I can also recall when I lost a bet because of a silly mistake I made. It was painful because my analysis was right but I erroneously picked the wrong teams. There was also an incident in a physical betting shop where an attendant placed the wrong games and it made me lose money.