Japan has produced a number of people who deserve to be called a “linguistic giant.” Sekiguchi Tsugio, I believe, is one of them. He is said to have begun reading a German version of Crime and Punishment as early as in his early teens. He referred to a dictionary countless times as he patiently read the book. He later became an expert of German but, as his books tell us, he was also conversant with other foreign languages.
He says in one of his books that if you want to master a foreign language, you need to make a tragic but brave decision: to isolate yourself from the rest of the world. I believe it is this resolution that is lacking in the people who complain that they can never make progress in English. However, living as I do in Japan, I often find this resolution harder than any other to keep. It seems that what is important is to spend some time, not all the time, in isolation and do it every single day.