When I was a kid, there was an obscure book I loved called Flat Stanley, which I had checked out of the library once but which no one else had ever heard of. I remember thinking that hiding in the picture in the museum was cool, but also being puzzled as to how his skull got flat without crushing his brain. No one could discuss these things with me, because no one else had read the book.
Fast forward 30+ years, and Flat Stanley is not only not out of print, it's now something every kid reads, and has, like, 5,000,000,000 sequels and projects schoolkids do, where they mail Flat Stanleys to far-away friends and ask for pictures of his travels. I don't know how this happened, but I'm pretty impressed. Somewhere at some publisher there's a marketing genius who I hope has been properly thanked.
Last month, Flat Stanley came to visit us, courtesy of my sweetie's friend's third-grader.
We had a good time :-).