Meaning
Outward appearance doesn’t reliably reveal someone or something’s true nature or value.
It’s used as a caution against snap judgments, urging a closer look before dismissing or underestimating something based on first impressions alone.
Origin
An early instance of the underlying idea appears in George Eliot’s 1860 novel “The Mill on the Floss,” where a character discusses a handsomely bound book, implicitly separating a book’s outward binding from its actual content. But the fixed modern catchphrase, in close to its current wording, is better traced to the 1946 American murder mystery “Murder in the Glass Room” by Lester Fuller and Edwin Rolfe, which used the line “You can never tell a book by its cover.” So while the metaphor of books and covers had circulated loosely for decades, the specific proverb as it’s spoken today is a mid-20th-century American formulation rather than a direct quotation from Eliot’s novel.
Examples
He looked unremarkable, but you can’t judge a book by its cover.
The shabby little restaurant served the best food in town — you can’t judge a book by its cover.
She seemed shy at first, but you can’t judge a book by its cover.
A: He doesn’t look like a chess champion. B: True, but you can’t judge a book by its cover.
Frequently asked questions
What does 'You can't judge a book by its cover' mean?
Outward appearance doesn’t reliably reveal someone or something’s true nature or value.
It’s used as a caution against snap judgments, urging a closer look before dismissing or underestimating something based on first impressions alone.