 Docter estimated it took four years of development for the film to achieve success in marrying the architecture of Riley 's mind and her personal troubles . The concept of " personality islands " helped develop the film 's emotional stakes , as they directly affect events inside her mind and in her life . In one draft , the characters fell into " Idea Fields " , where they would " cultivate new ideas " , much like a farmer would cultivate crop . The character of Bing Bong — a discarded old imaginary friend — came about in one draft of the film as part of a refugee camp inside Riley 's mind . It was difficult to achieve the correct tone for the film ; for example , viewers could not be distracted by Joy 's nature or feel negative about the mess she helps steer Riley into . Rivera credited the casting of Amy Poehler , in addition to the idea of moving , with helping the film find the right tone . 
