The Book of Five Rings
Musashi was a swordsman of unparallelled ability. He was never defeated in 60 duels and wandered Japan seeking out the finest masters of combat available. The resulting strategy is a basic guideline on how to win which can be applied to much more than just swordsmanship.
The writings on strategy over technique, decisiveness, adaptability versus dependence, and the elimination of the unproductive reveals ideas that could be thought about for decades.
Today is victory over yourself of yesterday; tomorrow is your victory over lesser men.