“Knock on wood” (or “touch wood”) is a superstitious phrase said in order to stave off bad luck. It’s a way of seeking protection against the envy of evil spirits and the anger of the gods, who take a dim view of humans being too proud to be properly grateful for their good luck. It’s a way to avoid tempting fate.
The custom may originate in Celtic or German folklore, wherein supernatural beings are thought to live in trees, and can be invoked for protection. The Pagans thought trees were the homes of fairies, spirits, dryads and other mystical creatures, and might knock on wood to request good luck, or to distract spirits with evil intentions. When in need of a favor or some good luck, one politely mentioned this wish to a tree and then touched the bark, representing the first “knock.” The second “knock” was to say thank you. The knocking was also supposed to prevent evil spirits from hearing your speech and stop them from interfering.
Another version holds that the act of knocking was to perk up the spirits to make them work in the requester’s favor. The evil eye and the concept of being jinxed are common phobias and superstitious beliefs in Iranian culture, for example, and Iranians traditionally believe knocking on wood wards off evil spirits.
In Italy, tocca ferro (“touch iron”) is used, especially after seeing an undertaker or something related to death.
The Latin version of the phrase, absit omen, dates from at least the early 1600s, when it is quoted by John Heywood in his collections of proverbs. In February 1905, The Syracuse Herald reported, “Neglecting to knock on wood may have been responsible for the weather’s unseemly behaviour today.”
In the US, in the 1700s, men used to knock on the wood stock of their muzzle-loading rifles to settle the black powder charge, ensuring the weapon would fire cleanly.
Now that is a sensible reason to knock on wood!
But maybe I’ll tap on my desk three times. Just in case.