《韩非子·喻老》
曾子说： 这话怎么讲？ 子夏说： 我在家里学习先王的道理，总会非常敬仰，出门后看见富贵的乐事又总会十分羡慕，这两种情绪在心里发生了斗争，弄不清谁胜谁负，所以瘦了。现在先王的道理终于取胜了，所以胖了。 
今先王之义胜，故肥。 是以志之难也，不在胜人，在自胜也。
Zeng Zi said: How do you explain that? Zi Xia said: When I study the principles of the former kings at home, I always feel very respectful. When I go out and see the joys of wealth, I always feel very envious. These two emotions fight in my heart, and I can't tell who wins and who loses, so I lose weight. Now that the principles of the former kings have finally prevailed, I have gained weight.