I've been on a documentaries kick lately. One in particular sparked my interest. It was about chaos mathematics. Doesn't sound very writerly, does it? However, believe it or not, it really gave me something to think about in terms of book marketing.
First, we're word people, so let's get a definition down. We usually equate chaos with complete randomness, but this is not the case.
Chaos theory:the branch of mathematics that deals with complex systems whose behavior is highly sensitive to slight changes in conditions, so that small alterations can give rise to strikingly great consequences. (Google) This is commonly referred to as the butterfly effect.
Book marketing and, therefore the success of a book, is one such system. Hundreds if not thousands of systems combine to create an extremely chaotic system that Joe Writer is plunged into and told to swim once he has a published book. This is why there are no 7 keys to making your novel a New York Times bestseller. Anyone who claims to know the secret to this is trying to take your money. Certainly you can do a number of things that will increase your success, but you can't forecast trends, you can't dictate what movies are produced, you can't foresee what people's disposable income will be, you can't predict what other books will be released, or any number of other variables.
While this could be discouraging, I find it encouraging. If you've worked hard at marketing and your book hasn't gone viral, don't feel bad. As authors do all they can to get our books noticed. We keep plugging away, in hopes that at some point this chaotic system will work in our favor. The longer and harder you keep at it, the better your chances. The more books you have in the marketplace, the better your chances. Don't give up just because your initial efforts aren't met with success. And please be extremely cautious about anyone who promises instant success, whether it would be vanity publishers, publicists, or marketing gurus. The system is just too complex to reduce it to a step-by-step process.