Shugyō: attaining mastery to perform a skill unconsciously.

The concept is about lifelong training. By investing a lifetime into a skill, you'll become a master at it. Your knowledge will be so profound and complicated that you won't be able to pass it on as a hack. And once you're at the stage of mastery, you perform the skill unconsciously. As an example, samurais fight with swords and there is no time to think during a sword fight. The body and the mind must respond immediately, and this instant response is the result of "shugyō."