Many years ago, I ran across this passage in a now defunct blog (BookAngst):

… In my experience, unwanted-by-the-marketing-department books are, in fact, books that the editor himself was either insufficiently passionate about, or for which the editor failed, finally, to demonstrate—above all, to himself—that he had a vision for how to publish it effectively.

(If you'd like to read the full post, it's still archived here.)

There are few publishing-insider sentiments I agree with more than this—because it's proven absolutely true in my experience.

If I'm passionate about a project, everyone hears it, sees it, knows it—and everyone gets on board, even if doubts linger in the background. Passion is infectious. (Of course, if nobody trusted my judgment, that passion would cease to make a difference, but let's assume editors keep their jobs because their judgment continues to be trusted.)

I am guilty (sadly) of telling quite a few authors, as well as agents, that a project did not survive a pub board presentation due to lack of sales/marketing enthusiasm. While I'm not lying, I'm also not conveying the full truth: That if I were 100% sold on the project myself, I would pull all kinds of strings to make it happen. I've done it on rare occasions (sometimes to wild success, sometimes to wild failure), but I only do it when I have that passion or vision.

So now you know the truth. What if you're given this reason for rejection? What can you do about it?

1. Do YOU the author have a vision for how to publish the book effectively? Have you conveyed this vision convincingly? If you have, can the editor explain the weaknesses in it?
   
2. Is your concept truly compelling, something worth an editor getting passionate about? Remember, editors put their reputations on the line when acquiring your project. If it doesn't sell down the road, that's a mark against their judgment.
   

Writers have a difficult road ahead if they're unable to quickly explain or convey passion for a book or book idea (or if they don't have an agent who can do so on their behalf). To be convincing, you need a certain awareness, the most valuable awareness, perhaps: what makes your work exciting and attractive to people, whether readers, editors, agents.