Write what you "know"...and feel.
I had a realization today about a project that I've been working on. I've had this concept in my head for a number of months and I really like it. The characters are well-rounded and interesting, the world is dynamic and beautiful, and the plot line is as tragic and complex as any I've ever created.
However, after looking at the market I decided to make a pretty big change to the story itself. I decided to take it from 3rd person point of view to 1st person point of view because that's what I saw when I looked through the shelves at bookstores. I thought that, in making this change, I would make my book more marketable and I ended up ultimately rewriting and number of months of work. But after making the switch, I found it hard to connect with the characters who had lived in my head for this long. They sounded different with the perception shift and they were essentially strangers. I hoped that with time, I could respark these deep relationships but it simply hasn't worked.
Writing to market is a fine business plan--and writing IS a business--but in an industry of creation you really do need to write what feels right. What you "know" in your gut is right for the story and your characters. I'm going back to the first bit of advice I ever got as a writer: write what you know.
My definition of "know" has been flexed but at the end of the day, this is an invaluable lesson. Time to go back to the drawing board.