Game Theory and Eternity

So, I was in Econ 602 several weeks back, and we were studying a type of game in game theory in which the game is repeated indefinitely (well named, an infinite game, as opposed to a finite game, which ends at some point). One thing you see in game theory is if the different parties to the game will come to a mutual beneficial cooperative agreement, which benefits both parties. Many times, the answer is no, as is the case in the famous prisoner's dilemma game, which is a very simple and often presented result of game theory. In any event, my professor said something which really hit me. He said something to the effect of, "In most cases, cooperation is not possible in finite game. Cooperation only occurs in infinite games." In the end, this is an important concept. In game theory it is true because of math, the size of one's delta, and other crazy stuff. In life, it is true because if we really believe we are going to have some sort of eternal relationship with someone, we will cooperate. I know the game is infinite, and I hope to act accordingly.