Sometimes the billions of neurons firing in our brains help us concoct elaborate scenarios. We imagine ourselves with a dream girl, or landing a dream job... an astronaut, a rock star, even a United States Senator. But fantasies can turn dark. You start to believe there's a monster under the bed, or evil forces are aligning themselves against us. All these fantasies, good and bad, stem from an evolutionary imperative. Out brains are exploring potential outcomes that might help us achieve our ...