> Trailers don't summarise the whole movie.
Some do. If they contain:
* the protagonist's set-up
* the antagonist's set-up
* an explanation of the protagonist's challenges
* the protagonist overcoming the challenges
* the nature of the twist
* (sometimes the twist itself is hinted at)
* any romantic relationship of significance is both shown
and the direction it ultimately goes is implied
* half the big awesome SFX scenes
* half the funny scenes
* almost every character of significance to the plot
then there isn't much left, I know almost all the key checkpoints, who has to be where and do what and what action has to occur. It's pretty much sketched out. There's minimal suspense because I know who can't die and who has to be where at the end of the movie.
> And even if you feel they do, knowing the outline of a movie isn't going to ruin the actual movie experience itself.
It definitely can. Part of a story is experiencing it for the first time, watching it unfold and not knowing what will happen. Trailers take that away from you. "Oh yeah, I've seen this fight sequence and heard that joke before" just doesn't carry the same weight. And when I have a checklist of people with places to be and action scenes to happen, I can predict things. "Well, I know there's going to be a twist because X has to fight Y in the streets and it looks like they're getting along OK as we approach 1h 20m mark."
There's minimal surprise left, which really hampers my ability to empathize with the characters and engage in the story.