Well, it can't be entirely inscrutable, now can it?
We manage to argue about it with each other ..
... and sometimes -- though less frequently than we would like -- we manage to hand over some of our common sense to our children, in part (I assume) because of what we say about it to our children.
So there is some reason to think that common sense is not wholly ineffable, completely otiose.
I like that word, "otiose." I hope I'm using it correctly. I mean -- roughly: "impenetrable to the mind's eye."