Native speakers often don't actively pay attention to grammar rules to the extent that non-native speakers do because native speakers often mostly rely on what intuitively makes sense to them. Non-native speakers, on the other hand, usually first learn the language through a set of rules and exceptions then afterwards develop an intuition for the target language.

For a non-native speaker, some mistakes can be hard to make because you've been studying for years to not make it. For a native speaker those mistakes may be easy to make because they got a gut feeling of what was right then didn't pay attention, care, or remember when it was corrected assuming it was corrected at all.

Hopefully this helps a bit. This is largely what I learned from studying German from a professor with a PhD in linguistics who loved to go on little linguistics rants and tangents. But it also comes from what I've observed in my efforts trying to learn German and Japanese. Hope I'm able to get my skill in either language to where you're currently at in English.