Reliable social clusters can make new relationships feel risky [causal]
Once you have a cluster of associates on whom you can rely, however, it might not seem worth the risk of developing new relationships. At its extreme, this might mean a society of close-knit families closed off to most of the rest of the world, as in the impoverished subsistence economies discussed in chapter 4.
Russell Hardin, Trust and Trustworthiness, loc. 606