Before I became a writer, I used to like this statement. I would use it to refer to people. I still totally agree with it except when it refers to what it should refer to which is the covers of a book. In that case, readers totally judge books by their covers. As an "author", I hate the phrase because I know now the importance of how having a good cover can change the success of a book.
As a reader, the first thing I look at is the cover. If it catches my eye as I'm trolling a publishers website, I'll read the blurb. It goes the same way if it's the opposite, if it's a terrible cover, I'll just pass it by. So every time a new cover comes in for my book, I just cringe. Is it going to be good? Am I going to like it? Is it going to help me sell my book? Is the cover model overused? Honestly, we know when we see the same cover model over and over again on the book covers. We become jaded after looking at the picture after a while. Here is a perfect example from my own meager "pool". I live in the smallest state in the US and my Romance Writers chapter is also probably one of the smallest. One of my books has almost the exact same cover as another writer in the chapter. The only difference is the background. The cover model is the same one, with the same pose and everything. What are the chances of that happening? She self-pubbed her novel and I went through a publisher. Don't get me wrong, I'm not knocking the cover. I have given approval on all of my covers. So ultimately, it falls on my judgment. But it really blew my mind. Don't you just want to roll your eyes when you see yet another Jimmy Thomas cover? He actually keeps a tally of how many covers he's on. The last time it came across my desk it was close to three thousand covers. The man is nice look, don't mistake that but is he the only cover model out there?
What it comes down to, is that our covers really help sell the book. We do judge books by their covers.