Having a simple way to put it doesn't mean it's easy to do right.

My native language don't have anything like articles. I frequently misuse a/the in borderline cases. Or just omit the article completely..

Yet gender is super easy in my language! Each noun has gendered suffix. Once you know the word, you know it's gender. Or once you know the gender, you know the suffix... :)

But it is easy once you understand :-)

A == non-specific The == specific

'A dog' could be any old dog.

'The dog' is a specific dog we know.

Thus

A == any The == thing

Perhaps I'm not clear where with this understanding it would trip you up. Can you think of an example?

Can't come up with anything on the spot. But sometimes I see text I wrote and think why I put "a" or "the" instead of vice versa. Sometimes it's just not clear enough wether this item is specific enough or not.

On the other hand, I omit article completely more frequently than using a wrong one. I find I have to consciously think if I should use an article and which article should I use. When I write/talk quickly without double checking, shit happens. Even after using English a lot for 2 decades, articles is just a foreign feature that I have to use consciously.

My wife is Korean and often asks me questions and, while you aren't wrong, the rules are way more complicated than that.

I'm trying to think of an example--do you have one by chance?

Sorry, I'm coming up short. But the theme, I think, is that there are a lot of cases where that sense of specificity isn't quite obvious to a learner, combined with the fact that in some cases the right choice is no article.