Better to stop short than fill to the brim.
Oversharpen the blade, and the edge will soon blunt.
Amass a store of gold and jade, and no one can protect it.
Retire when the work is done.
This is the way of heaven.
-- Lao Tsu, Chapter Nine, Tao Te Ching, translated by Gia-Fu Feng.
(posted as an adjunct to Taking a Play Off)