The Book of Five Rings

The Book of Five Rings (???, Go Rin no Sho) is a text on kenjutsu and the martial arts in general, written by the Japanese swordsman Miyamoto Musashi around 1645. Many translations have been made, and it enjoys an audience considerably broader than other martial artists and people across East Asia. For instance, some foreign business leaders find its discussion of conflict and taking the advantage to be relevant to their work in a business context.
The modern-day Hyoho Niten Ichi-ryu employs it as a manual of technique and philosophy. Musashi establishes a "no-nonsense" theme throughout the text. For instance, he repeatedly remarks that technical flourishes are excessive, and contrasts worrying about such things with the principle that all technique is simply a method of cutting down one's opponent. He also continually makes the point that the understandings expressed in the book are important for combat on any scale, whether a one-on-one duel or a massive battle.
Descriptions of principles are often followed by admonitions to "investigate this thoroughly" through practice rather than trying to learn them by merely reading.