【日中则昃】〖rì zhng zé zè〗[As soon as the sun reaches the meridian it declines; decline after reaching the zenith]

日干夕惕著诗典，

中流击楫汉英翻。

则复剥极灭私制，

昃食宵衣大同寰。

太阳到了正午就要偏西。比喻事物发展到一定程度，就会向相反的方向转化。Sun will be west by noon. Metaphor when things develop tocertain extent, will transform in opposite direction.