The Wikipedia disambiguation page for the commonplace partial phrase “rule of three” lists nine items. Actually it lists 10, the tenth not being an example of the concept of the rule of three in day-to-day life but the title of a play; it may have been added by an editor simply to amuse himself or herself. (It was not me.)

It would be a perfect example of the rule of three to have three sets of three things make up the possible definitions of the phrase; it is comic to have 10 instead. So, why three wishes? Why do we knock on wood three times for good luck? (Does anyone knock for bad luck? There are a lot of people on our planet and even more have existed and departed; someone must have.)
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