Inciting incident
The inciting incident is the event that breaks a character out of their normal life and sets the story in motion. Here is what makes one work and where it belongs.
The inciting incident is the event that knocks a character out of their ordinary life and starts the actual story. It is the body found in chapter two, the letter that should never have arrived, the offer that cannot be refused. Before it, you have a situation. After it, you have a plot.
A good inciting incident does two things at once. It disrupts the normal you just established, and it raises a question the rest of the book exists to answer. The reader should finish that scene wanting to know what happens next, because something is now at stake that was not before.
Where it belongs
The inciting incident usually lands near the end of act one in a three-act structure, after enough setup that the disruption means something. Open too far before it and the story feels slow. Skip the setup entirely and the disruption has nothing to push against. The art is in how little groundwork you can lay before you light the match.
Why it matters when planning with AI
If you are outlining with AI, the inciting incident is one of the first beats to nail down, because everything after it is consequence. A plan with a vague or missing inciting incident produces a draft with no engine: events happen, but nothing drives them. Fix it on the beat sheet and the rest of the outline has something to build from.
See how the beats fit together in how to outline a book with AI.