你不是我怎能知道我没心
[nĭ bù shì wŏ zĕn néng zhī dào wŏ méi xīn]
'If You Are Not Me, How Would You Know I Have No Heart' expresses the sentiment of loneliness or isolation, implying that unless someone stands exactly in their shoes, no one can truly understand the feelings inside them, suggesting they may appear indifferent or apathetic.