那些痛苦谁知道那些伤心谁知道
[nèi xiē tòng kŭ shéi zhī dào nèi xiē shāng xīn shéi zhī dào]
Reflects innermost personal experiences of pain and sorrow one might not want to share. Expresses the difficulty of conveying or understanding deep emotions such as grief. Suggests feelings are private and unspoken.