PBW has another useful (at least to me) entry on tweaking your book proposal for maximum wattage. Number 5 of “Things That Slog a Proposal” is my favorite:
Not enough passion for the story. Don’t write anything just to write it. Write it because you love it. Because you can’t stop thinking about it. Because you get a thrill every single time you open the .doc file. Because if you talk about it at the dinner table one more time, your family is going to stab you in the heart with their forks. That kind of passion.
Because if you don’t love your story (and I’m not talking about an egotistical love that is blind to all its flaws), then no one else will. And why would you expect them to? When I was writing my first book, I did not know if anyone but me would ever see it, but I wrote like I was in love, for the sheer joy of putting pen to paper (or in my case, fingers to keyboard). I’d wake up every morning at six or so and just plop myself down in front of the computer and I would stay there – for the entire day – just writing. No distractions, no nothing. Just me and the computer. You can’t do that every day unless you love it (actually, you can’t do that every day unless you have the luxury of time, which during that period of my life, I did).
Writing is a party of one in the purest sense of the word, and unless you are driven by passion (at heart, passion, though I will admit to occasional bad days), then you will find it very difficult to have any measure of success (because it is just you, your drive, your desire). Of course, the same is true for any profession, but I think some jobs just require more out of you than others. Writing is one of them.
Of course, you don’t really need passion to get by in life. But it helps.