Why do you knock on wood for good luck?

Knocking on wood for good luck is believed to originate from ancient pagan cultures, particularly the Celts, who thought that spirits resided in trees. By knocking on wood, individuals sought to ward off bad luck or invoke the protection of these spirits. The practice has evolved over time and is now commonly used to prevent jinxing a positive situation or outcome. It reflects a blend of superstition and the desire for reassurance in uncertain circumstances.