from The Live Giving Sword, Secret Teachings from the House of the Shogun by Yagyu Munenori, translated by William Scott Wilson. All emphasises are mine.
When there is nothing at all left in your mind, everything becomes easy to do. The study of all Ways is done for the sake of making a clean sweep of your mind. Because in the beginning a man knows nothing at all, he has nothing at all in his mind.1
When you begin to study, there is something in your mind; you are obstructed by that thing, and it becomes difficult to do anything at all. If you can clear from your mind those things you have learned, they too will become nothing; and when you perform the techniques of the various Ways, the techniques will come easily regardless of what you have learned and without being contrary to it. When you perform an action you will be in harmony with what you have learned, without even being aware of it.
You should understand that this is the Way of the martial arts. The heart of “extending knowledge” is the discipline of exhaustively learning a hundred methods with the sword and thoroughly mastering the postures, methods of using the eyes, and the other techniques.
When you have run the length of various practices and none of those practices remain in your mind, that very lack of mind itself is the heart of “all things”. When you have exhaustively learned the various practices and techniques and made great efforts in disciplined training, there will be action in your arms, legs, and body but none in your mind; you will have distanced yourself from training, but will not be in opposition to it, and you will have freedom in whatever techniques you perform. You yourself will be unaware of where your mind is, and neither demons nor heresies will be able to find it. Training is done for the purpose of reaching this state. With successful training, training falls away. This is the secret principle towards which all Ways progress.
By forgetting about training and casting off your mind, you will be all the more unaware of yourself. The place you come to in this way is the perfection of the Way. At this level, you enter through training and arrive at its very absence.
1 Implying not the general lack of skill of such a man, but rather his freedom to act and react naturally without being shackled by any ‘techniques’.