Musashi on Mind and Wisdom

Do not let your mind become clouded inside; keep it broad, and place your wisdom in that broad place. It is very important to polish both the wisdom and the mind earnestly.

Sharpen your wisdom, distinguish principle and its opposite in the world, learn the good and bad of all things, experience all the arts and accomplishments and their various Ways, and act in a way so that you will not be taken in by anyone. This is heart of the wisdom of the martial arts.

...Even when the action is extraordinarily lively on the battlefield, you should that the principles of the martial arts to the extreme and keep your mind unmoved.