On occasion, I have found some very old books (in thrift stores!) by some of the greatest Classical Musicans which helped me to understand better ways to play & teach. Although it's about playing Violin, "Six Lessons with Yehudi Menuhin," (the great Violinist) helped me to deal with playing some of my various instruments despite injuries. I fiddle a little (very little) with a fiddle, but I'm not at all a fiddler!
One out of print autobiography of a violinist taught me that it is wasteful to use only part of the rosin-instead of making the deep groove in the middle of a cake, use it all up. oh, duh!
I have found that these great Classical Musicians have been through many difficult life challenges & persevered, becoming better people & better at performing & teaching.