Tao Te Ching: Chapter 9
When the Tao prevails in the world, they send back their swift horses to (draw) the dung-carts. When the Tao is disregarded in the world, the war-horses breed in the border lands.
There is no guilt greater than to sanction ambition; no calamity greater than to be discontented with one's lot; no fault greater than the wish to be getting. Therefore the sufficiency of contentment is an enduring and unchanging sufficiency.