The rule in this game is that it's a one-time only situation.  The intention is to screen out any anticipation of reciprocity.

A repeated scenario would look pretty much, I'd say, like the iterated prisoner's dilemma

The classical prisoner's dilemma:

Two suspects, A and B, are arrested by the police. The police have insufficient evidence for a conviction, and, having separated both prisoners, visit each of them to offer the same deal: if one testifies for the prosecution against the other and the other remains silent, the betrayer goes free and the silent accomplice receives the full 10-year sentence. If both stay silent, both prisoners are sentenced to only six months in jail for a minor charge. If each betrays the other, each receives a five-year sentence. Each prisoner must make the choice of whether to betray the other or to remain silent. However, neither prisoner knows for sure what choice the other prisoner will make. So this dilemma poses the question: How should the prisoners act?

In this one-off situation the rational choice is to betray, because your rational colleague will have come to the same conclusion...

However, when the situation is repeated, between two or many participants, co-operation tends to evolve:

when these encounters were repeated over a long period of time with many players, each with different strategies, greedy strategies tended to do very poorly in the long run while more altruistic strategies did better, as judged purely by self-interest.