It's not necessarily that it's intractable - just that a thing can be very hard to describe, under some circumstances.
Imagine someone learning English has written "The experiment reached it's conclusion" and you have to correct their grammar. Almost any english speaker can correct "it's" to "its" but unless they (and the person they're correcting) know a bunch of terms like 'noun' and 'pronoun' and 'possessive' they'll have a very hard time explaining why.
They may not even know why and it may be okay -- they speak it somehow, right? In this case, the language is both a set or rules and a systematization of a pre-existing phenomenon. There's enough ephemeral, hard to explain concepts, but most humans just aren't used to explain it even to themselves.
For example, I've never learned English, anywhere. I know it from .txt and .ng documents and a couple of dictionaries I had back in the DOS days. I'm an uneducated text-native, basically. But here's what I'd say to that newbie:
- Usually we use "...'s" for attribution like in "human's cat = cat of a human". But "it" and other special words like "that", "there", etc are an exception. We write "it's" as short for "it is", sometimes "it has". But we write "its", "theirs" for attribution, like in "its paw" = "paw of it" ~~ "cat's paw" = "paw of a cat". There's more to this, but you can ignore it for now.
Imagine someone learning English has written "The experiment reached it's conclusion" and you have to correct their grammar. Almost any english speaker can correct "it's" to "its" but unless they (and the person they're correcting) know a bunch of terms like 'noun' and 'pronoun' and 'possessive' they'll have a very hard time explaining why.