WARNING: If you haven't seen any of the Marvel movies, or if you're behind in your viewing, there may be storyline spoilers for you in this post.
The world of comic books is all about continuity; a hero does this thing in his book which in turn may affect several other books over the course of months or even years moving forward. Though there has always been a certain level of continuity required in the movie industry, it hasn't really ever had as much detail.