On paper, One Day should have worked: It was based on a best-selling book, adapted into a screenplay by that book's author, and directed by a woman who'd scored a Best Picture nomination for her last movie, An Education. And yet, critics were rough on the romantic drama, which pulled in a meager $5.3 million in its opening weekend. Why did One Day falter while the adaptation of another popular novel, The Help, has turned into a late-August hit? Can the imprimatur of a best-selling book only get you so far at the box office? Or are there some novels that simply lose their magic when they're adapted for the screen?