People generally don't take a few math classes and expect to become a mathematician or some physics classes and expect to become a physician. At some point, they realize they reach their limitation and will tell themselves "I have enough of that" and move on. This is not true for language learners. This group is a special bunch. After a couple of years of learning a language, they usually get upset when they don't improve any further because invariably their expectation is to become a native. Anything less won't suffice. For some odd reasons, the difficulty of mastering a language does not exist like it does in the other fields of study. If I were a language, I would be offended because people think I am so easy.
By the way, that physics classes and physician bit is an attempt at humor.
Phil, you raised a good point. We were born into our first language. Most people forgot about that.
Vera, being understood is what most learners could ever hope for. It is my goal.