If we concentrate only on developing "finger technique" and neglect music during practice, we can pick up non-musical playing habits. Non-musical playing is an absolute no-no at all times because it is one form of mistake. One common symptom of this mistake is the inability to play the lesson pieces when the teacher (or anyone else!) is listening. When an audience is present, these students make strange errors that they didn't make during "practice". This happens because the students practiced without regard for music but suddenly realized that music must now be added because someone is listening. Unfortunately, until lesson time, they had never really practiced musically! Another symptom of non-musical practice is that the student feels uncomfortable practicing when others can hear them. Piano teachers know that students need to practice musically in order to acquire technique. What is right for the ears and the brain turns out to be right for the human playing mechanism. Both musicality and technique require accuracy and control. Practically any technical flaw can be detected in the music. At the very least, the music is the supreme test of whether the technique is right or wrong. As we shall see throughout this book, there are more reasons why music should never be separated from technique. Nonetheless, many students tend to practice neglecting the music and preferring to "work" when no one is around to listen. Such practice methods produce "closet pianists" who love to play but can't perform. If students are taught to practice musically all the time, this type of problem will not even exist; performing and practice are one and the same. We provide many suggestions in this book for practicing to perform, such as video taping your playing from the very beginning.
Many students make the mistake of thinking that the fingers control the music and they wait for the piano to produce that gorgeous sound. This will result in a flat performance and unpredictable results. The music must originate in the mind and the pianist must coax the piano to produce what s/he wants. This is mental play, introduced above; if you had never practiced mental play before, you will find that it requires a level of memorization that you had never achieved before – but that is exactly what is needed for flawless, authoritative performances. Fortunately, mental play is just a few steps beyond the memorization procedures in this book, but it accomplishes a giant leap in your musical capabilities, not only for technique and making music, but also for learning absolute pitch, composing, and every aspect of piano playing. Thus technique, music, and mental play are inseparably intertwined. Once you are deeply involved with mental play, you will discover that it doesn't really work without perfect pitch. These discussions provide a firm basis for identifying the skills we need to learn. This book provides the practice methods needed to learn them.
from "Fundamental of Piano Practice"