It depends. Probably some of them have their basis in fact: it is a bit dangerous to walk under a ladder because the person up the ladder might drop something on you! But usually superstitions are nonsense – they are harmless things people say. As long as you don’t take them too seriously then they are no problem.
I certainly believe that people have them, but usually they’re not true. In fact that’s the definition of a supersition – a belief without evidence. If there were evidence then it wouldn’t be a superstition it would be a sensible thought.