The ceramics teacher announced on opening day that he was dividing the class into two groups. All those on the left side of the studio, he said, would be graded solely on the quantity of work they produced, all those on the right solely on its quality. His procedure was simple: on the final day of class he would bring in his bathroom scales and weigh the work of the quantity group: fifty pound of pots rated an A, forty pounds a B, and so on. Those being graded on quality, however, needed to produce only one pot -albeit a perfect one - to get an A.
Well, came grading time and a curious fact emerged: the works of highest quality were all produced by the group being graded for quantity. It seems that while the quantity group was busily churning out piles of work - and learning from their mistakes - the quality group had sat theorizing about perfection, and in the end had little more to show for their efforts than grandiose theories and a pile of dead clay.
Art is human; error is human; ergo, art is error. Inevitably, your work (like, uh, the preceding syllogism) will be flawed.
What you need to know about the next piece is contained in the last piece.
I have nothing to add. Buy the book.