A lot of trailers I’ve seen lately give the whole story. But they have gotten away from juxtaposing two scenes that have nothing to do with each other and making them seem as though a lead character got blown up during the movie.
Maybe. I know that the previews for the television series "Mad Men" show a lot of "on-screen drama" -- doors slamming, snarling, knowing looks, raised voices, and threats -- but notoriously don't give any clue as to what will actually happen next week.
I wonder if there's a psychological or brain science dimension. A preview might show me everything that's in a movie, but in such a way that I'm more bowled over by the sheer experience of the thing and not working to put the pieces together.