Be Nice and To Forgive in a Long Term Battle

I usually only gets one point from one book, but a seemingly second point in "Selfish Gene" has been very sticking in my mind.

The essense of it is: in a long term relationship, the seemingly optimum strategy is like a tic-for-tac strategy -- it starts with a "nice" behavior toward an "opponent", then repeats the behavior of its opponents (toward it). The author summarize 3 properties of tic-for-tac strategy: 1. Be nice. we start being nice to others. 2. Be forgivable. We don't remember others "bad" for long. As soon as other start being nice to us, we are nice to others. 3. There is no end to the relationship. We don't see when we will never see the others.

As a result, the majority of the people on earth are nice. And as a result, I should be nice and forgivable to ultimately win our life.