One day he left home to go study with this great Zen teacher.

"I want you to teach me your art and help me become one of the best martial artists in the country," the young man said. "How long must I study?"

"About ten years," the master answered.

Impatiently, the student answered, "But I want to master it faster than that. I will work very hard. I will practice everyday, ten or more hours a day if I have to. How long will it take then?"

"In that case it will take twenty years," replied the master.

The young man was distressed. He asked again, "But what if I practised day and night with all my effort, then how long would it take?"

"Thirty years," was the master's response.

The young student became angry. "Why is it that each time I say I will work even harder to reach my goal, you tell me that it will take longer?"

"The answer is simple," the master replied. "With one eye focused on your destination, there is only one eye left with which to find the way."

Most versions of this story are much shorter. I like this version because it kind of gives you the moral rather than making you work for it. Not very Zen of me ;)

For the curious, here's the most common version: