FIFTY SHADES OF GREY began its unlikely success story as Twilight fan fiction—an online phenomenon where fans of preexisting books, movies, or TV shows pen original stories about the characters from those works. These new stories can’t be sold because they use copyrighted characters, but they’re often shared for free online. Eventually, author E. L. James rewrote her fan fiction and self-published it as Fifty Shades of Grey; it was then picked up by a traditional publisher and became an even bigger hit, doubtless inspiring fan fiction of its own. Saul Loeb/AFP/Getty Images