《文心雕龙·养气》
至于人的才能，都有一定的限度，而智力的运用却是无穷的；有人对自己如鸭般的短足胫感到惭愧，羡慕鹤的长足胫，练辞运意，呕心沥血，于是消耗精气，像水流到无底洞；神思损伤于外，像牛山上的草木被砍得精光。
若夫器分有限，智用无涯；或惭凫企鹤，沥辞镌思。于是精气内销，有似尾闾之波；神志外伤，同乎牛山之木。
As for a person's abilities, there is a certain limit, but the application of intelligence is boundless; some people feel ashamed of their short legs like a duck and envy the long legs of a crane, practicing rhetoric and devotion, and putting their heart and soul into it, so that they waste their energy, like water flowing into a bottomless hole; the mind is damaged by the outside world, like the vegetation on Niushan Mountain being chopped down.