Socialism fails because of the tragedy of the commons—a kind of prisoner’s dilemma. The impossibility of foretelling others’ behavior leads to fellows putting short-term selfly benefits ahead of overall long-term gains.

Socialism also often leads to idleness: a fellow is not incentivised to work hard when he will reap the same benefits regardless.

But families are socialist by definition, yet remain unfazed by the issues above. That’s because socialism can work in a fellowship that is not merely voluntary, but also fully conscientious. Quite hard to achieve outside of family.