Many of our superstitions came to us from very ancient sources. The idea that one should knock on wood for good luck, for example, is a 4,000-⁠year-⁠old custom that began with some Native American tribes of North America. Noticing that the oak was struck often by lightning, members of the tribe thought that it must be the dwelling place of a sky god. They also thought that boasting of a future personal deed was bad luck and meant the thing would never happen. Knocking on an oak tree was a way of contacting the sky god and being forgiven for boasting.

Another interesting superstition is that it is bad luck to open an umbrella indoors. In eighteenth-⁠century England, umbrellas had stiff springs and very strong metal spokes. Opening one indoors could indeed cause an accident. It could injure someone or break a fragile object. This superstition came about for practical reasons.