He who knows the male (active force) and keeps to the female (the passive force or receptive element) Becomes the ravine of the world. Being the ravine of the world, He will never depart from eternal virtue, But returns to the state of infancy. He who knows the white (glory) and yet keeps to the black (humility), Becomes the model for the world. Being the model for the world, He will never deviate from eternal virtue, But returns to the state of the Ultimate of Non-being. He who knows glory but keeps to humility, Becomes the valley of the world. Being the valley of the world, He will be proficient in eternal virtue, And returns to the state of simplicity (uncarved wood).

(Lao Tzu)