One should not form an opinion on someone or something based purely on what is seen on the surface, because after taking a deeper look, the person or thing may be very different than what was expected.
Example: There’s a new coworker at my job. At first, I thought he looked mean, like a tough guy that you wouldn’t want to joke around with. But after talking to him, it turns out he’s really nice and has a great sense of humor. This is a good example of the saying: “Don’t judge a book by its cover.”
If someone is looking for a book to buy and read, the first thing that will probably grab their attention is the cover of the book. Based solely on the cover, a person may decide whether a book is or is not for them. As a result, they may overlook a book simply because the cover appears plain or uninteresting to them. However, if the person would have opened the book up and looked at what was inside, they may have found it to be pretty interesting after all.
This expression is also applied to people. How so? Well, people are often judged based only upon their outward appearance. However, if one were to get to know the person and see what’s on the inside, ‘opening’ the person up, so to speak, then that one may be pleasantly surprised to find that the person is very different to how they imagined. Hence, this expression is used either as advice or a warning that a person should not judge other people or things based only on what they see on the outside.
Anyways, this phrase goes back to at least the mid-19th century. It makes an appearance in the newspaper Piqua Democrat, June 1867:
“Don’t judge a book by its cover, see a man by his cloth, as there is often a good deal of solid worth and superior skill underneath a [???] jacket and yaller pants.”
A small thing to note here is the print in the newspaper I was looking at was small and thus it was hard to read. Even so, I tried quoting it as accurately as possible. At least there was enough clarity to make out the phrase for sure.
- Pineapple is a delicious fruit, but it never appealed to me because of its hard and spiky exterior. However, after a friend cut a slice for me to eat, I learned that you shouldn’t judge a book by its cover.
Note: Sometimes, the origin of popular sayings is not clear. If that happens, what you’ll usually see on the phrase’s page are theories that talk about where it may have come from.
Additionally, the quotes you’ll see are typically the oldest I could find. These come from old books, poems, or newspapers, etc. Keep in mind, though, that there could be older recordings that I missed.