The Sword is the mind.

When the mind is right,
The Sword is right.
When the mind is not right,
The Sword is not right.
He who studies the way of the sword,
Must first study the way of the mind.
– Unknown
Be true to the thought of the moment and avoid distraction. Other than continuing to exert yourself, enter into nothing else, but go to the extent of living single thought by single thought.
– Yamamoto Tsunetomo