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Luck, Placebos, and Superstition

How expectations can change our luck.

Key points

  • "Knocking on wood" is a superstitious ritual that can be traced back to the Pagans.
  • In one study, half of the subjects "knocked on wood" when asked personal questions, while even more did so when asked about a stressful event.
  • The more stressed out one is, the less control one has—and the more likely one is to turn to ritual and superstition to compensate.
  • Howard Brody suggests that there might be a link between rituals and the placebo effect.
Photo by RODNAE Productions from Pexels
Source: Photo by RODNAE Productions from Pexels

Professor Giora Keinan at Tel Aviv University studies superstition. In one study (2002), Keinan was interested in the old superstition about knocking on wood—I’m sure you know it. When someone suggests that something bad might happen, something that we have no control over, knocking on wood, touching wood, or simply saying “knock on wood!” turns that bad thing away from us. Sometimes we invoke the ritual when we’re wishing for some bit of good fortune to come our way. Touching wood is seen as a way to avoid the bad luck that wishing for good luck might bring.

Knocking on wood, or just touching wood is an example of an “apotropaic” ritual (apo from the Greek meaning “away” and trepein from the Greek for “to turn away.”) An apotropaic ritual is one that is designed to keep harm or bad luck away from the individual performing the ritual. Scientists who study the origins of superstitions trace this one back to the Pagans who believed that spirits lived in trees. Touching the tree, or knocking on it, alerted the spirits to your request to keep the bad luck away, or maybe served as a distraction so that a spirit intent on harming you or your family forgot his or her evil intentions.

Keinan interviewed students under two different conditions. The first group of students were under a lot of stress—they were about to take a major exam. The second group of students served as the control group and were interviewed on a regular, “no-test” day.

During the interviews, both groups of students were asked a series of questions. Some were target questions, asking about cancer in the students’ families, about serious car accidents where a fatality might have occurred, and about the students’ health in general. They were also asked some filler questions about their favorite TV show and the sports they played. The filler questions were there to keep students in the dark about the real purpose of the study, so they wouldn’t change their answers to the target questions. The interviewer paid very close attention to whether the students’ knocked on wood (or even just said “knock on wood” out loud). Then the students’ filled out a questionnaire designed to measure their desire for control of events in the world around them.

Results of the study

First, half of the 108 students in the study knocked on wood and most of them knocked when asked about cancer in their families (cancer is tough to deal with). The more stressed the students were, the more likely they were to knock on wood and the higher the desire for control was, the more likely the student was to rap on the wooden table. In general, the more stressed out we are, the less control that we have, the more likely we are to turn to ritual and superstition to compensate.

Howard Brody (2010) suggested that there might be a link between rituals and the placebo effect. Both rely on the expectation of a result for their effectiveness. The stronger the expectation of the effectiveness of a ritual or a “medication,” the better the outcome actually is. Brody defines rituals like knocking on wood as deliberate, intentional actions that we engage in to bring meaning to the world. The placebo effect is a change in our health caused by some symbolic or ritualized aspect of treatment. Both work, although not for everyone, because of our expectations.


Brody, H. (2010). “Ritual, Medicine and the Placebo Response,” In: W. Sax, J. Quack, and J. Weinhold, (Eds.) The Problem of Ritual Efficacy, pp. 151-167, Oxford University Press.

Keinan, G. (2002). “The Effects of Stress and Desire for Control on Superstitious Behavior,” Personality and Social Psychology Bulletin, 28, 102-108.