再美的小三也是妾
[zài mĕi de xiăo sān yĕ shì qiè]
This is a critical view on third-party relationships (cheating). Even if someone ('third party'/lover outside marriage) tries their best, they'll never achieve legal wife status. The word used means concubine, referring back to ancient times when emperors had many wives and concubines who were lower-ranking than wives. It implies an extramarital lover has no place.