"'Yes, and what a number of books I have, haven't I?' said Sylvester affably, closing the door. 'No, I have not, I believe, read them all.'" —Georgette Heyer, Sylvester, or the Wicked Uncle
You know how it is. You go to a bookstore in search of something new. You are full of good intentions. You will not overspend; you will not head for the same old genre authors; no, you will find that holy grail of avid readers, the thing you want to read next.
After a pleasant hour of hunting and gathering, you cull your stack to two or three. You head for the cashier, full of a sense of virtue at your restraint in replacing all those other delightful possibilities on the shelves. But then—alas for your good intentions!—your eye falls on the very next book in that mystery series you adore, the one you've been waiting to read for months and months . . .
At home you reason with yourself. Of course, after all that waiting, it is only fair that you should be allowed to read the mystery right now. After that you will read the next book, the one you went out for. And, most likely, you do. That's where it all starts.
Because the third book—the one that wasn't next and wasn't the mystery—has been passed over. It is not of your flock. It has acquired a stink. It is, in short, a goat. “Not that one,” you think, wrinkling your nose as your hand floats past its spine, “not today.” So there it sits, until you remember almost nothing about it except that it's one of those books you just don't ever seem to feel like reading. Not reading that book begins to feel deliberate and clever. "Oh, you've got Angle of Repose," someone will say. "Yeah," you'll respond, feeling superior, "Stegner's not really my thing. Too, I dunno, authentically-Western or something."
Still, when the time comes to purge your collection—at the very moment you should be separating the sheep from the goats—you pass over that same damned book. “I can’t get rid of that one,” you say to yourself. “It was supposed to be pretty good.” Persist in this behavior for a couple of decades and you have a multi-shelf problem on your hands. Ask me how I know.