"What happens in very many cases is that a custom arises from a humdrum and everyday usage or practice. As times change and there is no longer a practical reason for keeping it up, there is the usual human reaction to go on doing the same thing, so people tend, consciously or unconsciously, to find a justification to keep on doing the same thing the same way."

Which reminds me of the story ...

Of the new bride who was excited to host Easter dinner for her new family, and planned to cook a ham according to the tradition of her own family. Using her mother's recipe, the woman cut the ham in two and simultaneously baked them in separate pans. However, when her husband asked her why the ham was in two pieces, the bride said, "I don't know. It's the way my mom always did it." So, the bride called her mother, who said, "I don't know. That's the way my mother always did it." So then the mother called her mother and asked why she baked the ham in two pieces. And grandmother said, "Because I didn't have a single pan big enough."