Joy keeps Riley happy and optimistic. Sadness processes loss and signals the need for support. Fear keeps Riley safe from danger. Disgust protects her from physical and social poisoning (like broccoli or embarrassment). Anger ensures fairness and justice. Together, they guide Riley's reactions to the world.

The film challenges the idea that we must always be happy. Sadness is revealed to be essential because expressing vulnerability allows Riley to connect with her parents and receive the support she needs. The climax shows that mixed emotions (Joy and Sadness combining) create deeper, more mature core memories.

Core Memories are pivotal life moments that define Riley's personality. Each powers a 'Personality Island' like Hockey Island, Goofball Island, or Family Island. When these core memories are lost or tainted, the corresponding islands shut down, illustrating how depression or trauma can disconnect us from the things that define who we are.

Bing Bong, Riley's childhood imaginary friend, sacrifices himself in the Memory Dump so Joy can escape. His fading away represents the bittersweet necessity of growing up—leaving behind childhood innocence and imagination to make room for adult complexity. It is one of the film's most emotional moments.

The subconscious is depicted as a dark, gated cave where Riley's deepest fears (like grandma's vacuum cleaner or a scary clown named Jangles) and unruly thoughts are locked away. It serves as a prison for things that shouldn't be in the conscious mind, guarded by two guards.

The Train of Thought is a literal train that delivers memories, daydreams, and ideas to Headquarters. It runs all over Riley's mind but stops when she is asleep. Its erratic schedule and derailment during the film symbolize Riley's turbulent mental state during her crisis.

At the end of the film, the control console in Headquarters is upgraded with more buttons and knobs. This visualizes Riley's emotional maturation as she enters puberty. Her emotions become more complex, no longer just single-note reactions, allowing for nuanced feelings like nostalgia or bittersweet happiness.

Pixar consulted with psychologists Paul Ekman and Dacher Keltner. While scientifically simplified (we have more than 5 emotions), the film accurately depicts how emotions organize thinking, how memory consolidation works during sleep, and the vital social function of emotions like sadness. It is widely praised by therapists.

The sequel introduces Anxiety (orange), Envy (teal), Ennui (indigo/boredom), and Embarrassment (pink). These arrive during puberty, reflecting the socially-driven, self-conscious, and complex emotional landscape of adolescence, shaking up the dynamic established by the original five.

The Abstract Thought processing center is a dangerous room where characters are deconstructed into non-objective fragments, 2D shapes, and finally single lines. It's a clever visual pun on the cognitive development stage where children begin to understand abstract concepts, moving beyond concrete thinking.