You don't typically learn grammar rules when you learn your native language, you just pick up on the way things are done without even knowing it.
Sure, as you get older you learn a bit more about grammar, but so much is ingrained, to the point that we put very specific structures in place without having any knowledge of it at all.
Take adjectives for example. Adjectives come before the noun in English, but what do we do when we have multiple adjectives describing the same thing - what order do you put them in?
As this twitter user points out, your brain already knows this, it's just that you don't.