We are beginning to understand the various ways musicians are susceptible to injury. Short of injury, incorrect practice does the opposite of what practice is intended to do; it teaches us to get better at playing incorrectly.

If you sit at a piano with a stiff body, you are practicing being stiff; if you move your fingers in awkward ways, you are improving your ability to move unnaturally; if you fall onto the piano when using your thumb, you are learning to lose your balance; if you hold onto the keys when you play, your fingers will become crippled; if you play with harsh tone or with weak tone, your tone will become always more harsh or weaker; if you practice without concentration, you are increasing your ability to play absent-mindedly.

A pianist becomes whatever he or she practices.
The definition of good practice is repetition of what can be done well, so as to give the body the habit of moving correctly. If you can do something well, repeat it 10,000 times. This is why we spend so much time in Book 1; we're teaching our bodies to do automatically that which our intellect already easily understands.

Make only the best tone in the world when practicing. Tone is, after all, produced by a body movement, so from the beginning we must get into the habit of listening to our own tone very carefully.

Practicing can never consist of only playing through entire pieces. Everybody can play a short passage slowly, hands alone, with better tone and technique than he or she can produce in entire pieces, up-to-tempo, with hands together. Tone can constantly improve by slow, hands alone practice.

Teachers teach how to practice; parents learn to supervise correct practice. Correct practice consists of good posture and balance, natural movement of the body, the best possible tone, and repetition of what can be done well. Slow practice does not take longer than fast practice. Slow practice is the only way to learn music quickly and securely with good technique.