As an author, you start out writing your book because you love it and, sometimes, you love it so much that you are afraid to let it go. One day you decide it's time and you finally release it out to the world. What happens next is that you get so caught up in the "process" that you forget how much you love your book. There is editing and rewriting. There are illustrations to do over. There is marketing and paperwork. You get caught up in pre-sales and chasing reviews. Slowly you forget how much you love your book because it is real WORK now.
And then, when you have almost forgotten, someone sends you a picture of his daughter sitting in her mother's lap, reading your book and you get goosebumps. You realize that your hard work has created a moment in someone else's life. And you love your book again because you finally remember.