Why do people have superstitions?

I wonder where they come from or why they started. I throw salt over my left shoulder if I spill any and if a black cat crosses my path I turn my hat around three times. If I don’t have a hat on (usually I don’t) I just make a circle around my head like I did have one. I don’t even know why I do these things, it’s a habit, I suppose. But I honestly worry about what would happen if I didn’t do the “ritual”. Some people think I’m nuts.