I must add a warning to music teachers. They will be horrified by this book. “I didn’t practice much and never went to my lesson fully prepared,” Mr. Hersch explains at the outset. Even in later years, he avoided the rote playing of scales and exercises: “I’m never sure what or how to practice, so I rarely do. But I seem to pull it together when the lights go up.” That may seem like a bad attitude for a professional musician, but I have a hunch that much of Fred Hersch’s greatness stems from avoiding over-preparation and embracing the risk-taking attitude jazz improvisation demands when played at a high level.