The package that arrives in Romancing the Stone which will send Joan Wilder (Kathleen Turner) to South America; the telephone call that informs Tom Cruise his father has died in Rain Man; the dinner at which Reese Witherspoon’s fiancé announces he’s dumping her in Legally Blonde — these are the catalyst moments: telegrams, getting fired, catching the wife in bed with another man, news that you have three days to live, the knock at the door, the messenger. In the set-up you, the screenwriter, have told us what the world is like and now in the catalyst moment you knock it all down. Boom!
