There are a few theories for why people say “knock on wood,” but the phrase most likely originated as a way to ward off bad luck or cast away evil spirits. That superstition dates back hundreds of years to pagan rituals, before world religions existed.
Long before Judaism, Christianity, Islam and other major religions spread through the world, there was paganism - an oft-misunderstood word. Many pagan beliefs centered around nature as spiritual, powerful, healing and holy. This was especially the case with trees. For example, trees were a part of Celtic rituals, and they were considered homes for their gods.
The idea is that, while asking for blessings from their gods, pagans would lay a hand on trees for a connection and energy. So, when you knock on wood, you’re essentially replicating an old pagan ritual meant to protect the “knocker” from evil spirits or bad luck.
It’s a worldwide superstition that ultimately can be traced back to the powerful and important influence of nature. You can find variations of “knock on wood” in many countries around the world: India, Iran, Italy, Romania, Bulgaria, Croatia, Serbia, Poland, Russia and the United States.