Many people confuse omens and superstitions. Most omens are true because they are based on constant observations of animal behavior, changes in the environment, and so on. (I think I could provide an example with a scientific basis, but I don't know any omens.) Superstitions, on the other hand, have no basis, at least most of them don't. So what if a mirror broke, or a black cat crossed the road? Why should things suddenly go wrong? It's probably just a random coincidence. I'm getting at the fact that I believe in omens (even though I don't know them :D), but not in superstitions.