Do you get crushed by every negative review? Feel a deep pain in your gut if someone doesn't absolutely adore your book? As an artist, it's natural for you to love your creations...but it's something you've got to avoid. Loving your books is dangerous.
Love's Labor Lost
I wrote, once, about falling in love with one of my books...and how it nearly destroyed me. Now I know that I should never love one of the books I write....I should love writing itself.
There is a difference, believe me. If you love your book, you're going to be sensitive about it. You're going to find it much harder to listen to criticism that may help you, and you're going to struggle to read and absorb those reviews you work so hard to receive.
What I'm saying is this: that book isn't going to love you back. Don't give your heart away to something that can't return it or even reinforce it. Don't love your books, love the work. If you love writing itself, rather than the stuff you create with it, you'll always be a writer. If you fall in love with a book, you may get your heart broken. And you may come really close to never writing again, which is exactly what happened to me.
Writing a book is a labor of love, but that doesn't mean you should love the book. You should like the book. You should enjoy reading it (because if you don't, no one else will). And you should definitely put a lot of labor and love into it...just don't fall in love with it. Keep your distance, and stay professional as a writer. This way, you'll always get better as an author...and you'll always be able to move on to your next book project.