Chapter 17, Part 4E - Chuang Tzu

"From the point of view of preference, if we regard a thing as right because there is a certain right to it, then among the ten thousand things there are none that are not right. If we regard a thing as wrong because there is a certain wrong to it, then among the ten thousand things there are none that are not wrong. If we know that Yao and Chieh each thought himself right and condemned the other as wrong, then we may understand how there are preferences in behavior.

"In ancient times Yao abdicated in favor of Shun and Shun ruled as emperor; K'uai abdicated in favor of Chih and Chih was destroyed. T'ang and Wu fought and became kings; Duke Po fought and was wiped out. Looking at it this way, we see that struggling or giving way, behaving like a Yao or like a Chieh, may be at one time noble and at another time mean. It is impossible to establish any constant rule.
~ Burton Watson translation via Terebess Asia Online ~

Go here to read the introductory post to the chapters of the Book of Chuang Tzu.