someone explain the: show the ending of a movie as the beginning trope: how it started and why it works?

Personally, I quite often think it doesn't work. Directors use it as a way to hook the audience into questioning 'how did things get this way.' My feeling is that if they need a hook like that to get people interested in their movie, the story itself isn't very good.

The only time I've seen it used well was in Memento. It worked there because it gave the audience a better perspective of the main character's view of the world (don't want to give away too much to avoid spoiling it).