I hear most of the people say let us forget the past or past is past when they commit mistakes or they had bad experience in the past. I can also hear these words in girlfriends/boyfriends, most of lovers quarrel are because of their experiences from past relationship.
We can list things or experiences in the past that we might have done in a different way. Other than learning through experience and trying not to make the same mistakes again, there is nothing to be gained by being upset about what you did or didn’t do in the past. If we keep ourselves focus and stick on the past especially when it’s not productive it will just give stressful, stagnant life and hold up the present life that might bring more joy and happiness.