Stephen Sniderman’s excellent 1999 essay, Unwritten Rules, in The Game Design Reader: A Rules of Play Anthology talks about the tacit agreement of unwritten (and impossible) rules required for any kind of play or game. He uses currency as an analogy - we all know the piece of paper is inherently worthless but don’t argue over it when we buy a carton of milk. We mutually agree that a dollar is worth a dollar.
Then, this sentence jumped out at me:
"The system works even though no one can explain it fully and even though we all know it could collapse at any moment if people stopped trusting each other or the system itself.”