"Don't judge a book by its cover." is a bad idiom, because bookcovers are desinged to represent the content of the book.

https://lemmy.world/post/2246201

"Don't judge a book by its cover." is a bad idiom, because bookcovers are desinged to represent the content of the book. - Lemmy.world

Yes, but you still don’t know if the content is good or bad.