A superstition is a widely held belief in supernatural causation leading to certain consequences if you do or do not do something at a certain time, or if something happens to you. I think you may have heard that it's bad luck if a black cat crosses your path. Or that you should knock on wood at times so that something bad doesn't happen. Or throw salt over your shoulder to make sure things turn out well. Bad luck comes in threes. Don't walk under a ladder... Where do these ideas come from?...