But the central message of the film, according to the actress, is that it's OK to be sad.
"Joy has been in charge for 11 years and is pretty comfortable being in the driving seat and assumes she's going to be there forever," she says, "and we find out very quickly that Sadness, Anger, Fear, Disgust - the other emotions - want a turn at the wheel."
Poehler adds: "I love the message of the film which is basically that no-one can be happy all the time - and that's OK. In fact, sadness may get you where you need to be.
"It's a very revolutionary idea, especially for parents who are constantly obsessed with their children's happiness, and in doing so don't often allow them to be in the moment and feel their feelings, and it's a great thing for children to understand, too."
When Riley's family move from Minnesota to San Francisco, the trauma pitches Joy and Sadness out of headquarters, leaving Anger, Disgust and Fear in charge.
Or, in other words, according to director Pete Docter, Riley starts becoming a teenager.