If we have to be very sincere to ourselves, we can accept that human beings naturally finds difficulty in forgetting pains and Offence, but quickly forget the good things you have done for them. So when we speak of forgive and forgetting, it is not totally common or particular in humans.
So you might ask yourself why is it so? Yes! going by this teachings, the servant of God let us know that, it is as the result of lack of Love among men. This is very true because when a man loves you, he or she tends to quickly forgive your offences towards him or her. That's probably because there is love among the people.
However, this isn't particular with most people because it is not natural for people to easily forget the bad things others do to them, while they may easily forget the good things that same people did for them.
They very answer to this is what the servant of God said already in this teaching, which is Lack of Love. I will encourage you to listen to the message properly and you will learn.