or even habit?
What if the "custom" is not beneficial for the people involved? Is it still "the great guide of human life"? It shouldn't be a custom that is the guide, it should be Godly principles. Just because something is done often enough to become a custom doesn't give it value. It used to be the custom of the Aztecs to sacrifice babies to their gods. Was that a "great guide"? Some people here in America think it is an ok custom to abort our innocent babies, is that a "great guide"?