Why do we forget bad feelings about memories faster? Fading affect bias (FAB).
On my undergrad graduation trip to Bali, we got ripped off by our travel agent and somehow missed all the good food and stuff at Bali. However, looking back now, I find it not a bad experience and even think it is pretty funny retrospectively.
It turns out that this is a psychological phenomenon called Fading affect bias (FAB), in which emotion associated with negative memories tends to fade faster than with positive ones. In other words, our happy memories keep us happy for a longer time, while our bad memories won't make us unhappy long. It's noteworthy that FAB only applies to the feelings of the memories, not the content. Therefore, we do not forget what happened in negative memories.
A popular explanation for the FAB is the need for healthy self-awareness and self-view. It's like a psychological immune system that serves as a healthy coping mechanism to improve the overall positivity of life.
I found it quite therapeutic to know that even though everything is transient, good things stay longer than bad ones.