Musashi #4 : Know the Ways of all professions

Wow.  this is a fine and wonderful principle for several reasons. 

1) First of all, if you re interested specifically in martial arts, this principle will lead you to investigate the question of excellence.  How is it that people succeed and fail in the world?  Excellence, and the pursuit thereof, is separate from any specific application.
2) Knowing the different ways that people earn a living helps us to understand human nature itself.  We all sell, we all produce.  We all attempt to protect the proceeds of our labor.  Understanding this, and the things that human beings do to try to increase safety for themselves and their famiies will help you to understand human motivations.  When you understand that, it is far easier to avoid conflict...and in essence, not NEED to fight as often.
3)  What if you are interested in the arts, say, writing?  Well, how much more obvious could it be?  The more you understand about different professions, the easier it is to write about them convincingly.
4) Moreover, remember that your customers make their livings in some way other than writing.  YOu must learn to communicate with people who see the world differently.
5) Being genuinely interested in other people makes YOU interesting.  You can always find something to talk about at a party--just ask questions about other people's lives.  Being interested in them make you automatically a less self-centered person.  and helps you build rapport rapidly. 
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But in my mind, the most important reason is to be continually searching to understand yourself, and the people around you.  Continually searching for the answer to the question: how can I improve 1% this week.  If you know a goood baker, ask her what makes her kitchen special.  Know a great Cellist?  Ask her how much she practises.  Keep asking these questions, and you will slowly get a picture of the road that leads to success in any field.  Don't believe me.  Go out and start asking!  Humanity itself is the best education in existence.

Steve