Among all the participants in the creation, distribution, and reception of music the individual with the keenest sense for the technique vested in a piece of music is always the performer. The impeccable technique of a masterpiece he transmits will be the most valuable stimulus for his own technique of re-creation; his performance will be carried along by the composition's perfection; his craving for the listener's satisfaction will most readily be crowned with success. Since, on the other hand, technical imperfections of a piece either prevent the performer from soliciting the listener's satisfaction or force him to cover by his own re-creative power the weaknesses the composer's inability has exposed, he is the one who suffers first and has to pay most dearly for others' faults. No wonder, then, that ordinarily he develops a judgment for technical quality which may at times appear biased, short-sighted, and directed by his own selfish purposes, but which in its uninhibited relation to practical needs is more realistic than the judgment of either the composer or the listener. The composer, busy computing the structural material, frequently loses direct contact with the effects his piece will release; and the listener is not interested in the technical arrangement of the dishes served as long as he derives any aesthetic satisfaction from consuming them.Paul Hindemith, A Composer's World, 120.
That's RIGHT. And, I'd venture to guess, this is why most of the successful composers of history were also able performers. As a performer, I've often observed Hindemith's principles in action; many times I've listened to a piece, sometimes repeatedly, and decided to learn it and play it in a church service. If the piece is poorly constructed on a technical level, I'll know it by the time I've prepared the work to a performance standard. Many times I've snarked about this to people after church services ("Well, the performance went all right but it's not that great of a piece"), who had no idea what I was talking about; they thought it was terrific.
Moral: The performer always knows best.
Subsidiary moral: Hindemith is too cool for words. As a composer, he's one of the dozen or so truly major masters of the twentieth century, but as a thinker and all-around musician, he beats everyone else hands down.