The three-act structure originated in the theater world, where plays are always written with this dramatic structure in mind. The basic idea is that a script is broken down into three pieces known as acts. Act one is the set-up. This is where the main characters and setting are first introduced. Within the first act is a very specific plot point known as the inciting incident. This is the moment that sets the story into motion after the exposition has been presented to the audience. A good example of this would be Tom Hanks’ plane crashing in Cast Away. Act one usually ends with a character making some kind of decision, which propels him/her onto the journey that awaits them for the duration of the story. Another way of looking at it is that the main character is forced to leave behind the world they know in order to enter into a new phase of their life. Luke Skywalker leaving Tatooine is a classic example.