When Amy Green's young son was diagnosed with a rare brain tumor, she made up a bedtime story for his siblings to teach them about cancer. What resulted was a video game, "That Dragon, Cancer," which takes players on a journey they can't win. In this beautiful talk about coping with loss, Green brings joy and play to tragedy. "We made a game that's hard to play," she says, "because the hardest moments of our lives change us more than any goal we could ever accomplish."