In a film, the inciting incident is the moment that kicks everything off. In his book A Hero With a Thousand Faces, it’s what Joseph Campbell refers to as the blunder that starts the fairy tale. Though he thinks there’s a subconscious significance to that, psychoanalyzing Hansel and Gretel. (51)
As Freud has shown, blunders are not the merest chance. They are the result of suppressed desires and conflicts.
It’s what sets the hero off on the adventure. It may be split into several elements: a set-up and pay-off. So in Star Wars, the set-up is when Princess Leia launches the droids into space with a message for Obi Wan Kenobi. The pay-off is when Luke Skywalker has bought the droids, and plays the message.
Usually the inciting incident occurs very early in the film, but it is sometimes necessary to introduce the characters first, so that the viewer is invested in their story and understands why the inciting incident is so remarkable. Rocky has a rather late inciting incident, but Robert McKee explains in Story why he thought that was the right decision. (202)
If ROCKY’s Inciting Incident were the first event we saw, our reaction would have been a shrug and “So what?” Therefore, Stallone uses the first half-hour to delineate Rocky’s world and character with craft and economy, so that when Rocky agrees to the fight, the audience’s reaction is strong and complete. “Him?” “That loser?” They sit in shock, dreading the blood-soaked, bone-crunching defeat that lies ahead.
There’s an additional element of set-up and pay-off. McKee suggests that the inciting incident is the film’s major dramatic question. It sets up an obligatory scene, a challenge that you know the hero is going to have to face, usually at the end of the film. For example, the sheriff’s discovery of the shark attack victim in Jaws means that he is going to have to fight the shark at some point in the film. (199) If the Inciting Incident of a western features a villain killing a boy’s parents, you know that there’s going to be a rematch at the end of the film when the boy becomes a man.
Due to the time constraints of telling a complex narrative in a relatively short amount of time, writers tend to economize, ensuring that every scene matters and that some scenes fulfill multiple purposes to the overall story. This often occurs with the inciting incident. An example would be the early scene in Batman Begins in which Bruce Wayne fell into the bat cave. It was his introduction to what would become his symbol. It also indirectly led to the death of his parents, as his reaction to a bat costume in the opera resulted in his parents leaving the performance prematurely and meeting Joe Chill in the alleyway behind the theater.