Great ideas often develop gradually after studying a problem at length--but not always. Sometimes, an insight hits like a bolt from the blue. For Archimedes, clarity struck while he was taking a bath. For Gustav Mahler, it came as the blades of his oars touched the water. And for Albert Einstein, it emerged while he was talking to a friend. Why do these moments of insight strike so suddenly? Why do they so often come to us when we are focused on something...