“I’ll tell you why it matters” he’d say, sternly. “You play like you practice. Practice sloppy and you’ll play sloppy.”
You’ll play like you practice. You’re not going to be sharp unless you practice being sharp. I’ve heard this again over the years.
A nice reminder of a lesson I learned years ago in high school band. Practice is about building muscle memory so that in a “real” situation, you fall back on what your body and brain are already used to do it. If you slog through practice, you’ll slog through real life.