北城以北思念未归南城以南思念未满
[bĕi chéng yĭ bĕi sī niàn wèi guī nán chéng yĭ nán sī niàn wèi măn]
It implies unfulfilled longing or missing someone deeply. 'Beicheng' and 'Nancheng' symbolize two different places or emotions, with one being unable to forget someone and still holding onto the past while the other side hasn't felt enough longing.