The Book of five rings, Musashi Miyamoto:
If you study a Way daily, and your spirit diverges, you may think you are obeying a good Way but objectively it is not the true Way. If you are following the true way and diverge a little, this will later become a large divergence.
This is the way for men who want to learn my strategy:
1. Do not think dishonestly.
2. The Way is in training.
3. Become acquainted with every art.
4. Know the Ways of all professions.
5. Distinguish between gain and loss in worldly matters.
6. Develop intuitive judgement and understanding for everything.
7. Perceive those things which cannot be seen.
8. Pay attention even to trifles.
9. Do nothing which is of no use.