开心时伴你那叫朋友伤心时陪你那叫姐妹
[kāi xīn shí bàn nĭ nèi jiào péng yŏu shāng xīn shí péi nĭ nèi jiào jiĕ mèi]
This phrase means 'the one who stays with you when you're happy is called a friend; the one who stays with you when you're sad is called a sister'. It emphasizes the importance of true friendship and emotional support.