The classic film Ghost Dog
: The Way of the Samurai directed by Jim Jarmusch with Forest Whitaker in the lead role keeps getting back to the book: Hagakure: The book of the Samurai
by Yamamoto Tsunetome
This book is well worth a read with compilation of the philosphies of Yamamoto Tsunetomo. Yamamoto Tsunetomo was a samurai in the early 1700s. who retired to a monastery after his master's death.
Quote from the introduction:
The book is interesting not so much for all of its philosophies, which run from the profound to the mundane to the absurd, but rather for the historical context in which it was written. By the time Mitsushige passed away in May 1700, Japan had been at peace for almost exactly 100 years. This left the samurai with the same problem facing our modern military: how do you remain a proud, disciplined warrior in times of extended peace?