In my newest article, I try to estimate how much input is actually necessary to get from basic English skills to fluency.
Few people realize that learning a language fluently is a much more memory-intensive task than, say, learning organic chemistry or the history of Europe at an expert level.
Let’s consider the number of facts you need to know to produce correct English sentences with ease. Certainly you must know the meanings and pronunciations of something like 10,000 words and phrases — something like the contents of a medium-sized dictionary. But this is only half the picture. The other half are thousands upon thousands of little facts which tell you when to use different words and how to combine them with other words.