There are so many things stacked against an author.
First there's writing your book. There's no time for it. You've got writer's block. All the creative ideas are gone. You have to critique other books so people will critique yours.
Then there's getting your book published. Queries are of the devil. Agents block your way. Publishers take forever. Nobody wants the manuscript. Someone else's book is always better than yours.
And finally, you're published. But now there are no sales. You have to blog and facebook and tweet just to remind people you're alive. You give hours of your time away so you can sell a book. You have to go out of your comfort zone to be a salesman.
Wow. No wonder authors are often grumpy people. In the midst of all this, the dream and allure of publication turns into, "Why am I writing another stupid book? This is pointless."
Oh writer-friend, get yourself to a writer's conference.
I find that I need a writer's conference every six months. The motivational high I get from one tapers off in the following four months, and by month six I'm lagging. But once I get there, the speakers and the experiences of other writers rub off on me, and suddenly I find I can do it again. It encourages me to know we're all going through the same thing. And then I see that my efforts aren't so bad, that maybe I'm even doing better than some.
Discouragement is a drug, and it debilitates your psyche. But you'll need help coming off it. Plan on a writer's conference. Don't know where to go? Check out Shawguides, a wonderful site with more conferences than you have the time and money to get to. I promise you'll leave encouraged. It's so worth it.