THE DESIRE FOR CLOSURE IN STORIES. When I was in college some fifty years ago a version of the original of THE THREE PENNY OPERA had been rescued and reconstructed. I was among the students who went into Chicago to the theater where it was being given a special showing. There were gaps and the movie trailed off, but most of the movie seemed to be there. I talked with a friend about the movie, who said that he had noticed that the audience had laughed an awful lot at the cartoon (which was a very ordinary cartoon). He asked whether I had noticed that too. I had noticed it.
He had a theory that the audience had stayed to watch the cartoon because they had been left up in the air by the way the movie had trailed off. Laughing at the cartoon had released their tension.
Since then I have thought that movies and plays need something to get the audience out of the theater at the end of the show.