This Open University site enables you to play the Prisoner’s Dilemma game online and see for yourself how trust enables cooperation — or not.

Another part of the site gets into the Dilemma in detail

The Prisoners Dilemma shows that, in certain circumstances, if the members of a group trust each other, they can choose a course of action that will bring them the best possible outcome for the group as a whole. But without trust each individual will aim for his or her best personal outcome - which can lead to the worst possible outcome for all.