用情未至深怎知非良人用情未至深怎知非良人
[yòng qíng wèi zhì shēn zĕn zhī fēi liáng rén yòng qíng wèi zhì shēn zĕn zhī fēi liáng rén]
This phrase means, if your emotions aren't deeply engaged, how can you know whether the other person isn't good? It suggests only through sincere affection can one truly understand another's nature. Note that the line repeats, probably as an emphasis.