Tao Te Ching - Lao Tzu - chapter 56
Those who know do not talk.
Those who talk do not know.
Keep your mouth closed.
Guard your senses.
Temper your sharpness.
Simplify your problems.
Mask your brightness.
Be at one with the dust of the earth.
This is primal union.
He who has achieved this state
Is unconcerned with friends and enemies,
With good and harm, with honour and disgrace.
This therefore is the highest state of man.
(translation by Gia-fu Feng and Jane English