海水不可斗量
see 人不可貌相,海水不可斗量[ren2 bu4 ke3 mao4 xiang4 , hai3 shui3 bu4 ke3 dou3 liang2]
人不可貌相,海水不可斗量
you can't judge a person by appearance, just as you can't measure the sea with a pint pot (idiom)
临海水土志
Seaboard Geographic Gazetteer (c. 275) by Shen Ying 沈瑩|沈莹