Are you afraid of cats?
The number 4?
The number 13?
Opening the umbrella inside a room??
These superstitions are VERY VERY weird and specific, but their origins are also VERY VERY weird and specific.
Some say that knocking on wood comes from the Indo-Europeans, or the ancestors of them, or the ancestors of the ancestors of them. They say that wood hosts spirits, and if you knock them, it’s the same as asking for their blessing, thus the superstition still lives on.
These superstitions also mainly comes from one source, Religion.
Like the number 13, it came from the last supper of Jesus Christ, where he invited 12 people to eat, right before his cruxification.
It said that having 13 people in a table is bad luck, it now continued as the number 13 being unlucky. Many buildings skip the number 13 too, to avoid bad luck.
It is just a saying of things, that we shouldnt do, like indonesian superstitions such as, dont sit in front of your door or if you dont clean your room you will marry a bearded man. xD
Also, if our parents dont say these superstitions we will most likely not even care about it, oppositely if they do these superstitions we will most likely obey them.
This is a matter of beliefs, and also if you know that knocking on wood gives you good luck, you might as well do it, because it’s easy.
Well, that’s it.
Conclusion is if our parents told us to believe it, we might as well do it. It’s all because of belief.
That’s all folks!