1.3. The prisoner's dilemma game is one of the most important models in all of social science: Most games of trust can be thought of as some kind of prisoner's dilemma. Here's the classic game:

Two men rob a bank and are quickly arrested.

The police do not have an airtight case; they have just enough evidence to put each man in prison for one year, a slap on the wrist for a senous cnme.

If the police had more evidence, they could put the men away for longer. To get more evidence, they put the men in separate interrogation rooms and offer each man the same deal: If you testify against your accomplice, we will drop all the charges against you (and convict the other guy of the full penalty of 10 years of prison time). Of course, if both prisoners take the deal, the police will have enough evidence to put both prisoners away and they will each get 6 years. And, as noted above, if neither testifies, both will get just 1 year of prison time. What's the best thing for each man to do?