In contemporary screenplay theory, every story must have an "inciting incident". The inciting incident is an event near the beginning of the story that initiates the protagonist on his or her journey. It represents a change in the equilibrium of the character. It has been described as an external event which creates a desire on the part of the protagonist,  the "primary cause for all that follows". 
Examples of inciting incidents are:
- In The Line Of Fire - Frank goes to an apartment to check on a routine call and discovers a serious threat to the life of the president that he must investigate.
- Stars Wars IV - R2D2 ends up in the hands of Luke Skywalker.
- Casablanca - Ilsa returns to Rick's bar.
As the above examples show, deciding which event is the "inciting incident" is somewhat arbitrary. In Star Wars, the inciting incident could have been Princess Leia putting the plans in R2D2 in the first place. Or, it could have been the Empire boarding her ship. Similarly, in Casablanca, Ilsa does not appear until almost thirty minutes into the story. Many important events have occurred before we even meet her. Are any of these events the "inciting incident"? If not, what are they? Many thoughtful screenwriting theorists and teachers do not place significant emphasis on a single event which begins the story.