Can you judge a book by its cover?
You can judge a book by its cover. Some people believe judging a book by its cover leads to false impressions.
The boys thought that the new scrawny kid could never be an athlete until they saw him on the basketball court. That just proves, you can't judge a book by its cover. Above someone wrote that story.They judged him by his appearance which is the basic meaning of you can't judge a book by its cover(it works with all nouns not just people)