“Sometimes a catalyst is situational, made up of a series of incidents that add up over a period of time. This sort of catalyst is rare, because hinting at action is usually not a strong way to start a story. Three films that have situational catalysts are Tootsie, Back to the Future, and Some Like It Hot. Tootsie, for instance, introduces the New York theater world, showing how difficult it is to get a job.”