What are examples of movies where the "sub-story" or "meta-story" mirrors the main narrative?

I just watched Black Swan, and I started to wonder about examples of other movies where the sub-story of the movie guides the main story.

Almost like the play within the play in Hamlet, but more comprehensive.

After seeing the movie I had the feeling that this is a common technique, and yet I couldn’t think of other examples.

Have any?