It would seem there's a reason people tend to believe in things like astrology and "the power of threes." To me, it looks like the old, "probability of something happening vs. the consequences of it happening" axiom in play. If being superstitious makes you less likely to get killed, then superstition will be selected for.

In other words, a smug assertion that rustling grass is caused by the wind will not impress the natives when a lion jumps out and eats you.