A young man named Matajuro wanted to become a great swordsman, but his father said he wasn’t quick enough and would never learn. So Matajuro went to the famous swordsman Banzo and asked to become his pupil.

“How long will it take me to become a master?”, he asked. “Suppose I become your servant, to be with you every minute. How long will it take?”

“Ten years.”, said Banzo.

“But my father is getting old. I’ll have to leave before ten years to return home to take care of him. Suppose I work twice as hard, then how long will it take me?”

“Thirty years.”, said Banzo.

“How is it that first you say it will take ten years. But when I offer to work twice as hard, you say it will take me three times as long?”, Matajuro continued. “Let me make myself clear. I will work unceasingly. No hardship will be too much. How long will it take me then?”

“Seventy years.”, said Banzo. “For a pupil in such a hurry learns slowly.”

Matajuro understood. Without asking for any promises in terms of time, he became Banzo’s servant. He cooked, cleaned, washed, and gardened. He was ordered never to speak of fencing or to touch a sword. Matajuro was very sad at this but had given his promise to the master and resolved to keep his word.

Three years passed for Matajuro as a servant. One day, while he was gardening, Banzo came up quietly behind him and gave him a terrible blow with a wooden sword. The next day in the kitchen, the same terrible blow fell again. Thereafter, day in and day out, from every corner and at any moment; he was attacked by Banzo’s wooden sword. Matajuro learned to live on the balls of his feet; ready to dodge at any moment. He became a body with no desires, no thoughts; only eternal readiness.

Banzo smiled, and began the lessons. And soon Matajuro was the greatest swordsman in Japan.

— Source unknown