Writers are notorious for lacking confidence in their work. Good reviews make us bounce off the walls. Bad reviews sink us in a terrible black pit of despair. So-so reviews leave us puzzled and worried... "What did she mean she wanted more tension? The hero and heroine nearly killed each other. Isn't that enough tension?"
When you have a lull between books, there's a tendency to feel like no one out there remembers who you are. Oh, your fellow authors are around, working to prop you up, but it's not the same thing as knowing that readers are reading your books. That's why reviews play such a important role for the writer, especially the new writer. It isn't the review per se, but the fact that someone read your book!
I think that's why we get so excited when a fan drops us a note or when we get requests for an interview. I always think of that Sally Field acceptance speech for her Oscar... "You like me, you really like me!"
I wonder when we reach the point that we don't wonder anymore? Is it at ten thousand books? Or twenty thousand? Or a hundred thousand? Does Nora Roberts go to bed at night wondering if her readers really like her books? Or will we always wonder, how ever successful we are, whether our readers will still love us when the next book is released?
The truth is probably that we will always have that little niggling doubt about our writing. There will always be that wince when we go back and read something that we wrote last year or the year before or even twenty years ago. That is life. But at this time and place people are still buying the books. They're still plunking down their hard earned money to read what we have to say. And that's proof enough for the most part.