Before the heavy thoughts I wanted to share an inspiring photo from my vacation. Now right into it:
That one's easy, a writer's business is to write, right? Wrong. A writer's business is to entertain. It's nice to think of writing a novel you are completely in love with and want to share with the world. Nice and unrealistic. The truth of the matter is, the public must be in love with it. If you are too then that's just a wonderful coincidence. I'm not saying don't write what you love, by all means please do. But if you want to make your writing a business you must make the public happy because when it comes down to it, writers are in the entertainment business. If our novel isn't entertaining to others, they won't buy it. Which means agents probably won't pick us up because they know editors won't buy it. That's where that vicious cycle of what's selling at the time comes in. Timing in the entertainment industry is why some really fantastic books get passed over.
If you've wrote a book you feel very confident about and it's just not selling don't get discouraged. It could just be your timing. What doesn't sell this year might sell next year. Shelve it, maybe do a little editing, then try again the next year. It's easy to get discouraged after dozens upon dozens of rejection letters. But remembering that it could just be your timing can take some of the sting out.
You can even go a step further into the entertainment industry and think about your book being made into a movie. Many of us dream of seeing our characters up on the big screen. But how to go about that? It isn't all up to your agent, in truth it's more up to your book. Some books just aren't going to make good movies and that's fine. But if you want your book to have a shot at it it's a good idea to think about that as your writing it. Here's some great advice on the subject from a literary manager: http://kenatchity.blogspot.com/2009/07/five-things-to-consider-when-writing.html
If you're not planning on making a business one day out of your writing then relax and just enjoy the process. But if you really want to dive into the entertainment industry start keeping track of what's selling in your genre, how its being marketed, and if it's being made into a movie. Best of luck!