Can't judge a book by its cover
不能仅凭外表判断人或事物，强调内在价值与表面不符。
提醒勿以貌取人或轻视外表普通的事物。
例句
He looks scruffy, but you can't judge a book by its cover; he's a genius.
典故来源
源自19世纪美国出版业，提醒读者勿以装帧判断内容，后泛化。