It’s just plain hard to get people working together the way you’d like. That’s because, left to our own devices, we are often too greedy and self-centered to collaborate, preferring instead to compete as individuals. Sigmund Freud made this point, comparing humans to hedgehogs in the winter: When hedgehogs get cold, they huddle together to warm up, but then things become unbearably prickly as they sting each other with their spines.