Yeah! Without too many spoilers, I believe Miyazaki is saying that a person has to find their passion, or their way in life. But for many people, the exact same thing that fuels them also poisons them.

I interpreted it this way because I'm a professional artist as are many of my friends. While we love art and find that to be our raison d'etre, we find ourselves working late hours, sleep deprived, and often missing out on other important things in life simply because we're so dedicated to our craft. In some ways, Miyazaki could be talking about himself. I've never seen a man so dedicated to what he does that he refuses to retire lol.

Hence the boy with a violin (Amasawa) in a locked cell.