The genesis of superstitions

Mistakes Were Made (But Not by Me) mentions a curious tradition among the Dinka and Nuer tribes of the Sudan - they extract the front teeth of their children.This gives them a sunken chin, collapsed lower lip and speech impediments. The practise started at a time when lockjaw (which causes the jaws to clench together) was widespread. Pulling out the front teeth meant that the children could drink liquids through the gap. The lockjaw epidemic is long gone but the practise continues. Why? In 'Mistakes Were Made (But Not by Me)' the authors write:

During the epidemic, the villagers would have begun extracting the front teeth of all their children, so that if any later contracted tetanus ,the adults would  be able to feed them. But this is a painful thing to do to children, especially since only some would become affected. To further justify their actions, to themselves and their children, the villagers would need to bolster the decision by adding benefits to the procedure after the fact. For example, they might convince themselves that pulling teeth  has aesthetic value - say that sunken-chin look is really quite attractive - and they might even turn the surgical ordeal into a rite of passage into adulthood. And indeed that is just what happened. "The toothless look is beautiful," the villagers say. "People who have all their teeth are ugly. They look like cannibals who would eat a person. A full set of teeth makes a man look like a donkey." The toothless look has other aesthetic advantages: "We like the hissing sound it creates when we speak." And adults reassure frightened children by saying, "The ritual is a sign of maturity." The original medical justification for the practice is long gone. The psychological self-justifications remain.

Perhaps many superstitions began in a similar manner. There may initially have been good reasons to start the practice. These reasons have been long forgotten but the justifications remain.