Miyamoto Musashi, the greatest swordsman of the Tokugawa era, wrote these 21 precepts one week before his death. Together they are called the Dokkōdō ("Way of Walking Alone").
I'm writing my thoughts on each precept both to digest them and so I can revisit this post a decade from now.
1. Accept everything just the way it is.
Live in reality. To accept things as they are means seeing them and absorbing them without preconception. Acceptance does not mean we do nothing. It is only when we accept a situation that we can thoughtfully decide what to do.
2. Do not seek pleasure for its own sake.
The Katha Upanishad makes the same distinction between the pleasant (preyas) and the excellent (shreyas). The pleasant is fleeting, but the excellent endures. "For its own sake" is critical: this precept is not asking us to be monks or mortify the flesh.
3. Do not, under any circumstances, depend on a partial feeling.
I think this means that when you must rely on intuition, do so only when you have a strong feeling. But if you second-guess your decisions temperamentally, this is terrible advice.
4. Think lightly of yourself and deeply of the world.
This is low-class. Thinking yourself higher than the world is solipsism and egotism. But thinking yourself lower than the world is martyrdom and another form of egotism. Both are dualism. When self and world are seen as non-dual, the distinction does not arise.
But as far as low-class statements go, it's a good one. The world is everything that made us: our friends and family, our cultures, our towns and countries, ... it is much more valuable than we are.
5. Be detached from desire your whole life long.
Preference and craving are not the same. Musashi here means "craving." This is a critical distinction.
6. Do not regret what you have done.
The past cannot be changed. Learn what you can and return to the present.
7. Never be jealous.
Nobody has the situation you do or the experiences you have had. From the start, nobody was playing the same game as you.
8. Never let yourself be saddened by a separation.
Easier said than done. But union and separation are the nature of life. Everything has a lifespan, which makes our time with it all the more precious.
9. Resentment and complaint are appropriate neither for oneself nor others.
Because neither translates to action. Act.
10. Do not let yourself be guided by the feeling of lust or love.
Concrete example of (2).
11. In all things have no preferences.
Rather, don't be attached to your preference. Don't be fixated on getting your ideal. Learn to enjoy and work with what you have.
12. Be indifferent to where you live.
Variant of (5) and (11).
13. Do not pursue the taste of good food.
Variant of (2), (5), and (11).
14. Do not hold on to possessions you no longer need.
Don't be a hoarder. You can't take it with you when you die, and it brings its own headaches. See George Carlin on Stuff.
15. Do not act following customary beliefs.
Tradition is powerful and useful, but it quickly becomes stale. Live in the world of today, not the world of 50 years ago.
16. Do not collect weapons or practice with weapons beyond what is useful.
"Useful" smuggles in a lot. More concretely, don't get so distracted with the lower games (tactics) that you lose sight of the higher games (strategy).
17. Do not fear death.
The future is uncertain. Foresee what you can and return to the present. Inverse of (6).
18. Do not seek to possess either goods or fiefs for your old age.
Variant of (14) focused on the future.
19. Respect Buddha and the gods without counting on their help.
As the saying goes: don't seek to be the master. Instead, seek what the master sought.
20. You may abandon your own body but you must preserve your honour.
I take this as a variant of (4).
21. Never stray from the way.
All you have is now.