In fact, it’s so common we often don’t think about it. But it’s worth asking: why do people who do not believe that knocking on wood has an effect on the world often do it anyway? Because it works.

No, knocking on wood won’t change what happens. The cancer is no more likely to stay in remission one way or the other. But knocking on wood does affect our beliefs, and that’s almost as important.

Research finds that people, superstitious or not, tend to believe that negative outcomes are more likely after they “jinx” themselves. Boast that you’ve been driving for 20 years without an accident, and your concern about your drive home that evening rises. The superstitious may tell you that your concern is well founded because the universe is bound to punish your hubris. Psychological research has a less magical explanation: boasting about being accident-free makes the thought of getting into an accident jump to mind and, once there, that thought makes you worry.

That makes sense intuitively. What’s less intuitive is how a simple physical act, like knocking on wood, can alleviate that concern.