"Inception" (2010) is a science-fiction heist film in which Cobb (Leonardo Dicaprio) and his team attempt to plant ideas in the head of a target by invading his dreams. In the beginning, the idea of a totem is introduced, which allows the characters to know whether they're dreaming or not.
Cobb's totem is a spinning top that never falls as long as he's dreaming. At the end of the film, Cobb has successfully pulled off the job and is reunited with his family while his totem spins in the foreground. It teeters slightly, but before it can fall the film cuts to the end credits. Audiences have argued whether Cobb was still dreaming or not by the end of the film.
Director Christopher Nolan told The Guardian that he personally doesn't feel as though it truly matters one way or the other: "The way the end of that film worked, Leonardo DiCaprio's character, Cobb - he was off with his kids, he was in his own subjective reality. "He didn't really care anymore, and that makes a statement: perhaps, all levels of reality are valid."
However, when pressed by actor Michael Caine for clarification while filming, Nolan let Caine know a helpful clue for separating reality from dreams. In an interview with TIME Caine revealed their off-screen conversation.
"When I got the script of Inception, I was a bit puzzled by it," Caine said. "And [Nolan] said, 'Well, when you're in the scene, it's reality.' So get that - if I'm in it, it's reality. If I'm not in it, it's a dream."
Because Caine's character is featured in the final scene, we can say definitively that Cobb is awake and happily reunited with his children.