曾经沧海难为睡除却巫山都是晕
[céng jīng cāng hăi nán wéi shuì chú què wū shān dōu shì yūn]
Once experienced vast oceans, one finds it hard to find true tranquility; beyond the misty mountains, there's nothing but confusion. This alludes to the idea that once you have encountered or achieved something truly remarkable, other experiences pale in comparison or leave one disillusioned or unsatisfied. It borrows metaphors from classical literature, suggesting deep yearning for a past experience, usually romantic.