The way our memory seems to work is about the same way the spider web works when it traps little water drops in the light rain: some things catch on and stay for a while and some hit stay for a moment and then go away. Eventually, all will fade.
What is really different is that we have one significant advantage: If we want, we can recall our memories, and will be able to do so with little effort most of the time. The problem with that is that we also catch bad stuff from time to time, and that is also easy to remember.
Since we cannot control what we trap in our "memory web" the easiest thing to do is to make the most out of the positive things and try to learn what we can from the bad ones.
From Get Closer!