Or if members of a group are not familiar with each other, no mutual aid occurs until they have been together for some time. As familiarity grows, individuals come to sense the reliability of each other. Furthermore, the expectation of an indefinite number of future meetings means that deception is a much less attractive option. The major message is this: in cooperative behaviour, conditions matter a lot.

XREF: Connects to game theory and the iterated prisoner's dilemma, where repeated play makes defection less attractive.

Diego Gambetta, Trust - Making and Breaking…, loc. 460