expression
don't judge a book by its cover
Proverb meaning that outward appearance or status does not determine true worth. Literally: 'A mountain is not to be honored just because it is high.'
彼は貧しい家の出だが、山高きが故に貴からずというように、とても立派な人物だ。
He comes from a poor family, but as the saying goes, 'a mountain is not honored just because it is high'—he is a truly admirable person.
A classical Japanese proverb using the literary attributive form 高き and the classical 故に (because). The exact origin is uncertain, but it reflects a common East Asian sentiment that external appearances are not the measure of true value.