I can remember when I first started learning Russian, having had no previous success with languages, I was full of self doubt about the amount on progress I could make. It's easy to forget how magic a skill speaking in a foreign language can seem to those living in a monolingual culture. At some point the level of doubt began to subside, but I do still wonder whether I will hit a brick wall, and whether an advanced level is actually possible for me. In the world of chess, where every player has a numeric score that quantifies their ability, eventually every player hits a ceiling in his rating - as I did after a depressingly short period of time. Also no matter how earnest you were in your training, unless you started as a young child you were destined never to reach a high level. On the opposite side of the coin, when it comes to karate, pretty much anyone can get to black belt if they train diligently for long enough, sure some people might get there quicker, but it's pretty much obtainable for all if they can persevere. So can anyone really reach fluency at an advanced level? What are the potential blockers that might stop you from getting there? If you feel you're on a plateau, do you wait it out, is there a problem that you can somehow diagnose, or perhaps you will be stuck there forever? How would you know?