 In late 2009, Docter noticed his pre-teen daughter, Elie, exhibiting similar shyness. "She started getting more quiet and reserved, and that, frankly, triggered a lot of my own insecurities and fears," he said. He imagined what happens in the human mind when emotions set in. The idea to depict it through animation excited Docter, who felt it the ideal form to portray "strong, opinionated, caricatured personalities." He began researching information about the mind, alongside Jonas Rivera, a producer, and Ronnie del Carmen, a secondary director. They consulted Paul Ekman, a well-known psychologist who studies emotions, and Dacher Keltner, a professor of psychology at the University of California, Berkeley. Ekman had early in his career identified six core emotions — anger, fear, sadness, disgust, joy, and surprise. Docter found surprise and fear to be too similar, which left him with five emotions to build characters around. Other emotions considered for inclusion during the development process were schadenfreude, ennui, pride, and hope. Keltner focused on sadness being an emotion that strengthens relationships. Both emphasized how emotions organize social lives and the structuring of interpersonal interactions.
