Knowledge given to the readers but kept from some of the characters can be just as powerful as knowledge given to some characters but kept from the readers.
I learned this via David Baboulene’s book, since I’d never actually seen Back to the Future before.
After the sequence where Marty gets sent into the past, the viewers already have the knowledge that Marty comes from the future, though none of the other characters (except Doc Brown later on) know this. In fact, it is imperative that they don’t.
Say, for instance, the movie had started with Marty already in the past and the viewers just as unaware of his time traveller status as the other characters. Ignore, if you will, the problems with the plot that could occur (no scenes where Marty talks about his time travelling and no clear goals).
Therefore, the story would end with a twist, revealing that Marty was a time traveller all along. However, there would be a great deal lost, namely the tension that would come with the knowledge that any moment, someone could become aware of Marty’s time travelling. As I’ve said before, tension is a pretty important part.
If the story had been swapped around like that, there could have been changes in protagonist or whatever the case might be, and the holes could be fixed and it could have been a great movie. I’m not saying that having a twist ending is bad.
What I’m trying to say is that you shouldn’t hesitate to give your readers insider info simply because you want a stronger end. In fact, you might be giving away tension because of it.