Dr. James Austin, a neurologist and philosopher (!), wrote an outstanding book called Chase, Chance, and Creativity -- originally in 1978, then updated in 2003. It's the best book I've read on the role of luck, chance, and serendipity in medical research -- or, for that matter, any creative endeavor. And because he's a neurologist, he has a grounding in how the brain actually exerts itself creatively -- although there is more recent research on that topic that is even more illuminating (more on that later).