But plenty of actors have accidentally spoiled plot points before, and Captain America: Winter Soldier actor Frank Grillo recently revealed that he has a flashback role in Avengers 4.
Part of this process is surprising the audience with plot twists, which the studio and its actors must keep under wraps.
The Marvel Cinematic Universe is one of the biggest franchises of film history, so the pressure is on to deliver a satisfying blockbuster with each new release.