A young, but earnest, martial arts student asked his new teacher: “I am devoted to studying your martial system. How long will it take me to master it?”
The teacher replied casually: “Ten years.”
The student wanted to learn faster: “But what if I really, really work hard at it? How long will it take then?”
The teacher thought for a moment. “20 years,” he finally replied
Source: Why Training Your Mind Is the Most Important Priority in Life
My Comments: Really good piece on mind training.