Knocking on wood is believed to be calling on spirits who can protect us from misfortune. These spirits are believed to live in the trees and by knocking on anything made of wood, we call on them.
Knock your knuckles on a piece of wood to bring good fortune or ward off bad luck. Since at the least the 19th century the phrase “knock on wood”—or “touch wood” in Britain—has been part of the vernacular The phenomenon has been traced to the Celts, an ancient pagan culture, who believed that spirits and gods resided in trees. Knocking on tree trunks may have roused the spirits and call on their protection, It also may have been a way of showing gratitude for a stroke of good luck. People might have 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.
British folklorist Steve Roud traces the practice to a 19th century children’s game called “Tiggy Touchwood,” a type of tag where players were protected from being caught when they touched a piece of wood such as a door or a tree. “Given that the game was concerned with ‘protection,’ and was well known to adults as well as children, it might be the origin of our modern superstitious practice of saying, ‘Touch wood,’” he argues.
Ancient people believed that evil spirts lived in trees. To scare them away they would hit the tree. This is where our custom of “knocking on wood” comes from – to hope that bad things won’t happen.
You must knock on wood 3 times after mentioning good fortune or the evil spirits will ruin things for you.
Turkish people often pull on one earlobe and knock on wood twice to ward off a jinx. Italians, meanwhile, say the phrase “touch iron” when trying to avoid tempting fate.