"Tit for Tat" is the most successful strategy not only in Computer Science and Game Theory. Back in the days of the Cold War, Axelrodt and his group were asked to develop mathematical models on cooperation strategies for the US government. He decided to start an open tournament and invited other researchers and programmers to send him their strategies for testing. And surprisingly, one of the most simple programs won - Tit for Tat!
In the tournament, two parties had to decide for each draw, whether to cooperate or to defect the opponent. Each of the combination received a certain "gain" for each of the parties. After a number of draws, the winner is the one with the highest gain.
Basically, Tit for Tat means to start with cooperation, and depending on the outcome of the oponents last reaction, return the same. It outperformed the more sophisticated programs, such as "leak exploring" ones as well as other greedy mechanisms. With ONE core assumption: The number of subsequent cooperations was not known before, hence suggesting a "long shadow of the future".
Not only is such cooperation strategy fun to play with in computers, but has its impact in real life.
In the trench warfare of World War 1, soldiers on each side of the frontier did often develop such "Tit for Tat" strategies - they would not shut during certain periods of the day, or would not really aim. They knew - if they killed an Enemy soldier, the enemy would respond alike. Only when the commanders became aware of that, the strategy had to be abandoned.
In nowadays big business and politics, legislation periods for politicians and scheduled turnovers for economy mamangers cast only short shadows of future, and therefore barely animate to think long ahead. The resulting short-sighted strategies might be successfull for today, but who thinks seriously about possible impacts in the long run?