If a warrior is not unattached to life and death, he will be of no use whatsoever. The saying that "All abilities come from one mind" sounds as though it has to do with sentient matters, but it is in fact a matter of being unattached to life and death. With such non-attachment one can accomplish any feat.
Every day without fail one should consider himself as dead.
Meditation on inevitable death should be performed daily. Every day when one's body and mind are at peace, one should meditate upon being ripped apart by arrows, rifles, spears and swords, being carried away by surging waves, being thrown into the midst of a great fire, being struck by lightning, being shaken to death by a great earthquake, falling from thousand-foot cliffs, dying of disease or committing seppuku at the death of one's master. And every day without fail one should consider himself as dead.
As said by the Boddhisatva Guan-yin, or Kannon, to the monk Tripitaka: "All should be known"