Case studies can tell us a lot about how we learn a langauge, and how we can teach a language. For more, take a look at Case Histories and the Comprehension Hypothesis by Stephen Krashen.
In the paper, he discusses several cases, but two in particular are the cases of Mr. Yeo, from Singapore, and Lomb Kato from Hungary.
In this video, sixty-four year old Yeo Yew-Hock tells us how his first contact with books was when his parents accidentally brought back a book in a bag of charcoal when five or six years old. You can also read about his experience in Language Magazine
And here is a video of an interview with the world famous Lomb Kato. Lomb Kato is a famous polygot from Hungary, who mastered 17 languages. You can see, she is well known in her native Hungary!
This is a short video from a Hungarian living in France talking about Dr. Lomb Kato.
This study I did, Impressive gains on the TOEIC after one year of comprehensible input, with no output or grammar study, shows impressive gains without “studying” English at all.
Mr. Tanaka is a former student, and the subject of my study. Here is Mr. Tanaka talking about his experience (In Japanese).
How did they do it? By self selected extensive reading, of course!