Don't Judge a Book By It's Cover...and a slight opinion

They almost always say that you shouldn't judge a book by it's cover...but you kind of have to hen you think it through.
So, the whole cove rbis usually one piece consisting of the front cover all pretty, the side with the name and author, then the back which consists of the occasional summary, bur mostly reviews.
I mean, reviews say a lot about a book, whether it's a review from a top company or even a fan view, the cover does really help you judge.
I mean, yeah, you really shouldn't judge anperson by the way they look. Like, take me for example. Yeah, I have a large nose, so people automatically say I'm of Jewish decent, but in which case I'm not.
Which then leads me to sterotyping, I mean, come on, really? Yeah, I have a large nose, but I'm of German decent, no where in my family tree are we aware that we were Jewish, but I just have my family's distinct part. In all honesty, yes, I do sterotyp, but who doesn't, but when you do stereotype, you are setting youaelf up for some harsh comments...
I guess judging a book and stereotyping are kinda the same...but nor?
I think?
Why must I always question myself??