你若知我心怎会不伤心
[nĭ ruò zhī wŏ xīn zĕn huì bù shāng xīn]
Translated directly as 'If you knew my heart, how could you not be sad?' This suggests a sense of sorrow or feeling misunderstood by someone, often used in situations where there is emotional hurt from someone who's supposed to understand and care for them.