March 11, 2011: A magnitude 9.0 earthquake struck Japan, triggering a tsunami that flooded the Fukushima Daiichi Nuclear Power Plant. Three reactor cores melted down in the worst nuclear accident since Chernobyl. But here's the complexity: Zero confirmed radiation deaths among the public. Yet 2,313 people died from the evacuation itself—more than died from the earthquake and tsunami in Fukushima. The evacuation prevented radiation deaths and killed people who would have survived. Both things are true. Japan's nuclear disaster asks questions we're still struggling with: How do you design for the unimaginable? When does protecting people from one danger create worse dangers? And how do you make life-or-death decisions with incomplete information?