Tao Te Ching - Chapter Forty-six
When the world lives in accord with Tao,
Fine walking horses can be retired form plowing the field.
When the world fails to live in accord with Tao,
Even pregnant mares are used as war horses,
And were forced to breed in the battlefield.
The greatest crime is to have too much desire.
The greatest disaster is not to find contentment.
The greatest mistake is to desire for endless possession.
Hence, when one is gratified with self-contentment,
True contentment can then long endure.