用情未至深怎知非良人
[yòng qíng wèi zhì shēn zĕn zhī fēi liáng rén]
It implies that until someone falls profoundly in love, they cannot fully understand if their partner is truly unvirtuous or not good enough. There's a belief that only deep emotions reveal people's true nature. This reflects an optimistic attitude, hoping true feelings will bring out the goodness in people or recognize someone worthy.