There must be millions if not hundreds of millions of people who study languages. Most of them are frustrated and do not achieve fluency. I believe it is the false friends of language learning that let them down.
These false friends are:
exercises and drills
vocabulary lists and books
Why are these false friends? Because they are not natural. They do not offer real communication in the language. I am sure that most people who are fluent in a second or third language did not learn from these false friends. They learned by listening, reading and communicating in the language on subjects of interests, in other words, for real. Maybe they learned from friends, from TV, or from movies or from necessity, but the key is that they were motivated to learn. They took over the learning process and did not rely on the false friends. Certainly I was only able to achieve fluency in nine languages by studying on my own.
Anybody out there with some language learning experience to share?