This is the typical scenario used to explain, in simple terms, the concept of Game Theory, and it goes something like this:
Two prisoners are on trial for crime and each one faces a jail sentence (or not) based on the options given to them:
– do not confess
Simple, but to the point.
If they both do not say a word, there is not enough evidence to convict either with a criminal act, and they each get a sentence of say two years. If one of them confesses, that prisoner gets a reduction in the sentence to 6 months, while the other gets 5 years. If they both confess, they each get a break and a sentence of 4 years each.
The optimal strategy is obviously for both not to say a word. The selfish strategy is for one to confess and hope that the other one will not do the same.
This might seem like a very simple example, but this simple example demonstrates the complexities of dealing with a system with multiple users with each user aiming for a selfish strategy.