Not a big fan of that one, I think some situations are out of your control however nothing would have gotten done in this world if everyone followed this moto.
i don't think he meant it as "do nothing." rather, he meant something more like accepting the world as it is given to you, accepting the truth instead of rationalizing, etc
acceptance is a big part of moving on
this isn't just an idealist guess on my part. just from the little I've read from his "Book of Five Rings" it's clear he was a pragmatist. his style/philosophy was essentially "do the best thing in the given situation," not different in spirit from Bruce Lee's style
If we did accept everything just the way it is, then we would have to accept ourselves the way we are, too. Since we are motivated by the pursuit of material possessions, comfort, good food, desire and pleasure (among many other things), then I am tempted to conclude that Miyamoto Musashi's work is a little bit self-contradictory.
This one is a bit of a double-edged sword (no pun intended) but the way I look at that precept doesn't preclude doing something to change the situation. It just means being willing to stare reality in the face and accept (eg. understand) it for what it really is.
However, I suppose the word "accept" usually conveys the idea of doing nothing to change to situation. It's all about how the words are defined, which leads to pseudo-philosophical nonsense. Moreover, I assume the text was translated from Japanese, and there's always something lost in translation.
Not being able to accept reality the way it is often leads to inaction. "We'd be able to refactor that subsystem if the other developers had written tests and documented, damn them!" [inaction follows]
Your also talking about a book written in 1645 not just another language. The translation to "accept" on Wikipedia is far from the original concept so focusing on our connotations of our word is missing the point. I would say "Look at the world as it is not what you want it to be." but that's longer and less catchy.
"In all things have no preferences." > "React to what is happening not just what your ideas let you to see."
If you are really interested in this concept, I highly recommend reading Katie Byron. All her work is about accepting life as it is.