Comment by hyperpallium2

Customs are contingent truths and can only be learnt from others: which side of the road to drive on, language, laws, etiquette. Neither pure reason nor empirical fact fully determine them. When you hear them in your social context, you adopt them unconsciously and uncritically.

Therefore people from a disjoint graph of social interaction have different customs, which aren't supported by fact or reason.

They are insane.