The fully-occupied, sensitive and intelligent 16-year-old getting acquainted with the Chopin G major Prelude puzzles out the fingering and the nuances in the different tonalities and their varying configurations of black and white keys. She hears that she cannot play the figure exactly the same way twice. I encourage her to keep noticing the differences and to relish them because it means that her fingers are inflecting the way a good actor inflects his or her lines: never mechanically repeating them but allowing all sorts of unforeseeable things to affect their timing and internal stress.

To me this is mature piano playing. It is fascinating. Better than perfect.