Knocking on wood (also phrased touching wood) is an apotropaic tradition of literally touching, tapping, or knocking on wood, or merely stating that one is doing or intending to do so, in order to avoid "tempting fate" after making a favorable prediction or boast, or a declaration concerning one's own death or another unfavorable situation.
A common explanation traces the phenomenon to ancient Celtic peoples, who believed it called on spirits or gods of the trees,[1][2] while Christians tie the practice to the wood of the cross of crucifixion.[2] A more modern theory from folklore researcher Steve Roud suggests it derives from a form of tag called "Tiggy Touchwood" in which players are safe from being tagged if they are touching wood.[2] The British version of the phrase "touch wood" has been traced back as far as the 17th century.[3]