WARNING: The following contains major spoilers for Soul, now streaming on Disney+.
Soul is about jazz musician and middle school band teacher Joe, who suffers a critical injury, so his soul takes a journey to try to return to his body with the help of another soul, 22. Along the way, Joe and 22 encounter an ally named Moonwind, a hippy who can traverse to the soul world. Moonwind explains that living humans who get lost in "the zone" are temporarily transported to the spirit realm, so he spends his time in the soul world doing what he can to help "lost souls" return to their rightful place. Essentially, humans lost in "the zone" and lost souls are two sides of the same coin.
Being in "the zone" is presented in a neutral light over the course of the film, with those in it not being praised or criticized. Humans can find joy and bliss while lost in "the zone," like when Joe gets so caught up in his jazz music. While this is an activity that brings him joy, the problem comes when this pursuit becomes all consuming. Joe falls into this when he feels like his life has no purpose outside the actions that bring him into "the zone," making it like an addiction that pulls him away from reality.
This is similar to what happens to lost souls, which are frightening, animalistic versions of their former beings. 22 and Joe see Moonwind and his comrades capture and calm a roaming lost soul and help return them to their purest form. In this case, the lost soul is a stock broker who is so consumed by their job that it no longer brings them joy. This also shows that lost souls can be human or pure souls.
22 ends up as a lost soul when she becomes consumed by her feelings of inadequacy and failure. The way she is caught up in the cycle of self-doubt is similar to how Joe gets caught up in "the zone." They are both consumed by an emotion, whether good or bad, so they get trapped by that feeling.
Being in the zone is generally a good thing, until it becomes one's only focus, and a soul, whether human or pure, becomes lost when they are so caught up in a cycle that it leads to them losing touch with the rest of reality. Being in "the zone" and being a lost soul are not that different; they are two sides of the same coin. Learning to find balance and joy in life is a key message of Soul that is clearly seen in the exploration of these two concepts.
Directed by Pete Docter and Kemp Powers, Soul stars Jamie Foxx, Tina Fey, Questlove, Phylicia Rashad, Daveed Diggs and Angela Bassett. The film is currently available on Disney+.