But What Does It Mean?

Early on, I made a point of checking my rankings on Amazon and Barnes& Noble. Very shortly after I started, I realized that Amazon rankings appeared to change hourly. Very, very shortly after that I realized that the rankings had nothing to do with actual sales, but rather how my books were doing compared to all the other books on Amazon were doing. It would be entirely possible, though highly unlikely, that if I sold only one copy of a book on Amazon in the space of an hour while nobody else sold any, then for one brief, shining moment I would be #1 on Amazon. But I would only have sold one book, for all that.
It's easy to figure out where the 'top' of the Amazon rankings are. I have no idea where the 'bottom' is. It's a lot like floating in the middle of the ocean, able to see partway into the depths, but is the bottom only a few feet beyond my vision, or am I floating above the Challenger Deep? I don't know, and there doesn't seem to be any reliable way to find out.
I also keep track of my ratings on Goodreads. Now this might strike some as strange, but I don't actually mind getting a poor rating from someone I've never heard from before. I tell myself that it means that my titles are attracting readers from across a wide spectrum, and therefore I'm going to get a number of readers who just don't care for my stories. This may be overoptimistic on my part, I admit.
However, the ratings are entirely subjective. A '5' or a '1' rating is fairly definitive, but a '3' rating probably means very different things to different people. So when I get a '3' rating, I ask myself: What does it mean?
When it comes to a review, I don't have to ask myself that question. It may be just as subjective as a rating, but it gives me details.