Besides all good references you see here, try to understand human beings as selfish creatures. Cooperation comes into being when you need to play with the same

Besides all good references you see here, try to understand human beings as selfish creatures. Cooperation comes into being when you need to play with the same person/team many more times, that is, iterative games. If other party, say, X just works with you for one time, X can use you and dump you, while being nice at the same time. However, if you and X are forced to work together many more times: X and you have to cooperate. It is easier to backstab than being openly inimical. Being openly inimical has both emotional and political costs; backstabbing is easy.