蝴蝶终究飞不过沧海桑田
[hú dié zhōng jiū fēi bù guò cāng hăi sāng tián]
A profound sense of melancholy comes from 'Ultimately the butterfly could not fly beyond the vast sea turned into mulberry fields', highlighting an unattainable dream despite efforts - just like butterflies unable to traverse immense oceans over time transforming vastly different landscapes across epochs.