人不可貌相小三不可斗量
[rén bù kĕ mào xiāng xiăo sān bù kĕ dòu liàng]
This Chinese idiom 'ren bu ke mao xiang, xiao san bu ke dou liang' combines two idioms. The first one means we should not judge a person by his or her appearance; while the second is less polite, implying a situation where infidelity is involved. Together it might be a reminder that people are unpredictable and complex.