I’m a serial knocker-on-wood, because who really wants to take a chance, right?

But ask anyone, be they superstitious or not, and chances are they won’t know where the phrase originated from.

Fear not, because StackExchange has some answers for you.

First up they quote Robert Hendrickson’s The Facts on File Encyclopedia of Word and Phrase Origins:

Why do we say knock on wood and tap wood or our heads after declaring that some calamity has never happened to us? The superstition is an old one and has many possible explanations, none sure. It may be of pagan origin, deriving from the practice of rapping on trees to ask protection from friendly spirits who were believed to reside inside.

Or it could be a Christian superstition similar to touching wooden crucifixes or rosary beads. One theory even holds that the practice comes from games like hide-and-seek in which players who succeed in touching wood are safe from capture.

A last far-fetched possibility is that the superstition is linked to a verse in the sixth chapter of Galatians: “God forbid that I should glory save in the cross of our Lord Jesus Christ.” You will be forgiven any vainglorious boast, according to this story, if you quickly recall the wooden cross Christ carried.

And then two further examples from other etymological works:

Express a wish that something will or will not occur…This expression alludes to an ancient superstition that literally knocking on or touching wood will ward off evil spirits.

“If your right hand itch, you will get money. You should knock on wood, according to the saying, “Knock it on wood,/It will come good.”

So is there a concrete agreement on where it comes from? Not really, it seems, but now you get to pick your favourite and wow your workmates at lunch.

You’re welcome.

[source:stackexchange]