Cue the ElephantsToday's Tune:
"That book is terrible. The only reason it's selling so well is because of great marketing."
I imagine we've all heard (or said) some variation of the phrase above. It's easy to explain a "bad" book's success away with marketing or celebrity, isn't it? After having worked in marketing, however, I know there's a lot more to it that that.
Here's the deal: dumping a lot of money into marketing and promotion can absolutely increase a book's exposure. More eyes will see it, more ears will hear about it, and more impressions will be made. But exposure alone will not sell books. Or any product, really.
What I'm saying is the very best marketing in the world (traditional or digital) cannot sell a product no one likes or connects with. A product sells because it has something people want. (Or because they monopolize the market. YOU SUCK, COMCAST. BTW.). Books sell because people get something from them. Entertainment. Butterflies in their tummy. Excitement. Education. Laughter. Whatever. Then they tell their friends. That's where most sales come from -- word of mouth.
People are more likely to purchase things that have been recommended to them by a friend, family member, or acquaintance, and people don't recommend things they hate. Publishing houses often take gambles marketing books that don't end up selling so well for whatever reason -- didn't connect with people, wrong subject at the wrong time, didn't hit the right combo of timing and luck, whatever.
This very argument has been made several times over about the Twilight series, the favorite punching bag of recent years. I'm sure you've heard it before. According to this stance, Meyer supposedly became a millionaire because of fancy-pants Big Publishing marketing dollars shilling her book everywhere. But here's the thing... not really. Her fan base alone contests this very claim. Regardless of anyone's personal feelings about Twilight and its sequels, those books sold because they connected with their audience.
Writers can get hoity-toity all they want and cry foul about the books they think "don't deserve" the attention and sales they get, but it doesn't change anything. Marketing can only do so much. Advertisements can only do so much. Books sell because they're offering readers something they want. Period. They want a magical world and an unlikely hero. They want a "perfect" romance with a happy ending. They want to laugh. They want to cry. They want action and explosions and teenagers slaughtering each other on live TV. (Okay, they probably don't actually WANT that last one, but it's a concept that makes for entertaining and heartbreaking fiction. Which they do want.).
All that said, exposure doesn't hurt. The first step is, of course, to write a book people will want to read and connect with. After that's done, you can't very well send it out into the wilderness and hope it doesn't get lost. Good books are overlooked every day, many times because no one even knew they were out there. You don't need big marketing dollars to spread the word about your book. Check out Amanda Hocking. That girl worked the social media angle like no one's business to her very obvious benefit. BUT. She also had a book (several books, in fact) that people wanted to read.
So, to summarize:
1.) Write an awesome book people will want to read
2.) Somehow, some way, publish that book and make it available to the public
3.) Promote it any way you can
4.) Have some luck on your side