Knock on Wood for Good Luck

The most commonly repeated explanation traces the habit to ancient pagan Europe, where various cultures, including the Celts, believed spirits or gods lived inside certain sacred trees, oak, ash, hazel, hawthorn, and willow among them. Knocking was thought to either summon a protective spirit's attention or, in a related theory, to make enough noise to drive away evil spirits who might otherwise overhear someone tempting fate by boasting about good fortune. Christian tradition later gave the same physical gesture a new meaning, touching wood as a stand-in for touching the wood of the cross, seeking God's protection instead of a tree-spirit's. No solid documentary evidence actually confirms either the pagan or Christian version as the true origin, and the practice may simply be older and more diffuse than any single explanation captures.