To not to be able to forgive and inability to take revenge keeps killing you continuously inside.

We see that sometimes we get into an altercation with somebody or somebody says something to us with which we start feeling that we are being looked upon down, we are being wrongly evaluated, other person is trying to hurt us intentionally or other person did something wrong with us when he had option of not doing it, then we get hurt. We get angry. We want to teach a lesson to other person. We keep doing a calculation within ourselves continuously about how to teach a lesson to that person or we keep doing several arguments within ourselves to prove to us that we are right. When we see/confront that person then it reminds us of that feeling of hurt again. Every action of other person his smile, his gesture, his walking style, his entire body language, his words everything looks negative to us. Everything in him increases our feeling of hurt. With time this feeling of hurt keeps multiplying. We also start seeing every previous action of that person as negative. The more we dig into our memories about our interactions with that person the more we hurt ourselves and increase the willingness to teach a lesson to that person. If other person is the one who has been close to me since a long time then it hurts me more.

If somehow we empathize with that person or feel that he did not intend to hurt me or he meant something else than what I assumed or he had no other option than what he did, then we restore our comfort.

We see that all this is happening, but why this is happening?

Feeling of Non-Acceptance for another human being is not Naturally Acceptable to a human being. Till the time a human being has this feeling of Non-Acceptance for another human being he keeps killing himself inside.

At least one is able to see that this feeling of Non-Acceptance for another human being is very painful. As I described above, all those things happen and keep your mind occupied. In fact when a human being has this feeling of Non-Acceptance for other human being he spends all his energies to come out of the pain which he is feeling out of that feeling of Non-Acceptance. To come out of this pain, he plans to take revenge, he comes up with several arguments in his defense and also to teach a lesson to other person, his feeling for other person changes, he starts undermining other person and several more such things happen.

The thing to notice here is, once we get a feeling of Non-Acceptance for other person we try to do several such things which I described above. In all those methods we may be able to secure our comfort with that specific other person for some time but the possibility of this feeling of Non-Acceptance to come within us still remains available, with that person or with some other person again. On the other hand suffering with this feeling of Non-Acceptance is not Naturally Acceptable to a human being, so there is a need to identify the root cause of the problem and work over there so that this feeling of Non-Acceptance never comes again.

The root cause of this problem lies in the inability to recognize the root expectation/desire within a human being and means to fulfill it. This root desire/expectation is of Unconditional Acceptance in a human being from others around. A human being by birth has this expectation of Unconditional Acceptance from others around but lacks the competence to give it to others.

His Acceptance for others remains dependent on others acceptance for him. A human being is not able to accept others  when they are not able to accept him. As soon as he feels that he is being unaccepted by other person then he also start getting a feeling of Non-Acceptance for that person and this feeling of Non-Acceptance hurts him and NOT the Non-Acceptance of other person for him. This can be verified by anybody or needs a verification by everybody.

So ultimately it is the feeling of Non-Acceptance within me which is the source of hurt/pain within me. What all I try to do is to either hurt other person or to convert the feeling of Non-Acceptance in other person for me into Acceptance, anyhow. This creates all problems like hatred, anger, jealousy, competition etc.

To understand Acceptance we need to understand ourselves, so ultimately it comes down to a problem of our own lack of understanding of ourselves.

So when there is Acceptance, forgiveness is automatically there. In fact Acceptance is the basis of forgiveness.

To understand Accepance, Trust, Respect and Relationships we need Knowledge. It includes understanding related to:-
Self
Family
Society
Nature.