Letting go has always been one of the hardest things for me to do. If someone wronged me in the past I am sure that the person who wronged me has long since forgotten about it. Me, on the other hand, still remember it and I fight to keep it festering inside of me.
Why do we do this? It is because of our ego. Learn to control this and you will have a more peaceful life and it won’t bother you so much the next time it happens.