From David Bayles and Ted Orland's excellent book Art and Fear:
"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 the 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 in the
"quantity" group: fifty pounds 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 the highest quality were all produced by the group
being graded for quantity. It seems that while the "quantity" group was busy
turning 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."