In the course and in her book, Positivity, Barbara Fredrickson explains her theory of why humans have evolved with positive emotions, which she calls the 'Broaden and Build' theory. According to the theory, negative emotions prepare us for one specific action. Fear prepares us to run or to fight while anger prepares us to confront someone. Negative emotions narrow our fields of view to deal with the problem at hand, but positive emotions do the opposite. Positive emotions help us broaden our awareness and build resources for the future.