The more you learn about language and "correct" writing, the more you discover the amount of rules that aren't taught in school (or not my school, any way).
For example, I was never taught what a transitive
verb is (see Wikipedia
if you don't know). But I notice this occasionally with my wife. (She's an immigrant, and with English as her third language, she does remarkably well, so much so that in casual conversation you wouldn't know she's not native.) But every once in a while she comes out with a clunker, all the more surprising because you can forget she's not a native speaker. And this is one of the common problems.
Another thing that most natives just get right from having heard it so much, but isn't really taught explicitly, is when a determiner is necessary. One of the things my wife finds most difficult is deciding when a noun needs a "the" in front of it.
Finally, there's an error that I see committed almost universally, and demonstrating how much it's not
taught, I don't even know what the correct terminology is. I think of it as parallelization of lists. When giving a list, the items in the list need to all be of the same part of speech and conjugation. For example: "My dog Buster likes to chase a ball and poops in the woods". This is incorrect. I need to either change "poops" to "to poop" so that the list of what Buster likes is all of the same type, or I need to change it to "... and he poops..." so that it's not a list of what he likes to