I teach a discussion class at an Eikaiwa English-language school, and we once had a discussion about an article called 10,000 hours.

The article was written based on findings in the book Outliers by Malcolm Gladwell. The premise of this article was that a person who devotes themselves to a trade, craft, etc. for 10,000 hours or more becomes a master of that activity.

The article primarily used musicians as a case in point, but the same rule applied to professionals of all types. For example, the Beatles had easily surpassed the 10,000 hour mark, playing together at small gigs, developing a stage presence, writing music that reaches people, and honing their craft, before ever becoming a symphonic sensation. Michael Jordan easily logged over 10,000 hours of focused basketball practice before making other professionals look like amateurs, winning six NBA championships and going on to arguably become the greatest to ever play the game.

There are so many case studies to validate the 10,000 rule: Venus and Serena Willams, Warren Buffett, Roger Federer, Muhammad Ali, Mozart, your local dentist, Arnold Schwarzenegger, your local doctor, Babe Ruth, Bill Gates—and the list goes on and on.

I think learning languages is no different. I truly believe that if a person of average intelligence, who can learn from their mistakes, were to devote four years to seriously studying a language (whether an adult or child), they would be fluent—or extremely close.