After reading Paul Hindemith's A Composer's World I came to believe that the composer's customer is the musician, and the musician's customer is the audience.
Since we may assume that the composer is herself first and foremost a musician, we can assume that she should know when a piece is in some way satisfying to play. The appropriate audience picks up on that, and the enterprise succeeds.
If she wants mostly to create something satisfying to play, she will keep at it until it is no matter how long it takes. If she mostly wants approval, then she may rush through writing the piece and having it come out half-baked. If she mostly wants to prove a point, then she risks being rejected and/or ignored.