Forgiveness was taught to us by our Lord Jesus Christ. The human's mind is not possessing the ability to forgive. It possesses a revenge mind. It is the mind that is always wroth with the other person because of what has been done unto him or her. We always want to pay back. We want to give eye for eye and evil for evil. But that is not the doctrines of the New testament in Jesus Christ. In Jesus Christ, we are taught to forgive those who offend us. We are to forget and not remember again.
In the law of Moses, everyone received recompense equally for whatsoever offense he has committed. There was no room for forgiveness. Forgiveness never existed in their dairy. That is where they learnt the law of eye for eye and tooth for tooth. We are not going to practice that again. In the New Testament, we express love towards others. It is a true love that does not put in minds what wrong his or her neighbor has done to him.
Why we find it difficult to forgive others is because we are not walking in love. If we walk in love towards our fellow humans, we will not remember the wrong things that such people do to us.