姑娘不知爱伤心少年不晓情伤人
[gū niáng bù zhī ài shāng xīn shăo nián bù xiăo qíng shāng rén]
This refers to young love's misunderstandings and heartbreaks, describing a situation where a girl cannot understand why a boy's ignorance towards her affection can cause her so much pain. It speaks about youthful innocence and emotional complexity.