Why do we "knock on wood" for luck?

In many cultures, it’s a common superstition for people to knock their knuckles on a piece of wood to bring themselves good fortune or ward off bad luck. Yet while the phrase “knock on wood”—or “touch wood” in Britain—has been part of the vernacular since at the least the 19th century, there seems to be little agreement on how it originated.

One common explanation traces the phenomenon to ancient pagan cultures such as the Celts, who believed that spirits and gods resided in trees.

Knocking on tree trunks may have served to rouse the spirits and call on their protection, but it could have also been a way of showing gratitude for a stroke of good luck.

Yet another theory is that people knocked on wood to chase away evil spirits or prevent them from listening in when they boasted about their luck, thereby preventing a reversal of fortune.

Christians, meanwhile, have often linked the practice to the wood of the cross from Christ’s crucifixion, History writes.

Other researchers consider knocking on wood a more recent phenomenon.

knock on wood