What we call legal processes, statutes, courts, sentences, is the only the final visible ritual whereby a society reaffirms the peace. The human psyche is programmed by evolution to spot anomalies. Consider how you react when some stranger does something really weird in your presence. In fact, it is very easy to attract attention and disturb adult humans by improper manifestations. This truth opens up studies of the layers of human conditioning, in which custom plays a big role.
People learn to walk and talk like their parents and friends.
At an early age the child observes displays of human emotions, expressions of judged valuation, and incorporations these styles into his or her own psyche. But customary law is not to be confused with custom. Increasing we hear about customary law, and it is about time. Written legal codes have done a hatchet job on traditional societies from the Babylonians to the present day. Not much of customary law remains, and many educated Americans are largely ignorant of the customary roots of their own legal system.