Christopher Nolan first came up with the idea for Tenet while making Memento 20 years ago.
The director has always been interested in exploring metaphysical themes in his work, and in his summer blockbuster Tenet, John David Washington stars as a secret agent who has to embark on a time-bending mission to prevent World War III.
However, Nolan reveals the initial kernel of the idea came to him two decades ago, as he worked on psychological thriller Memento with Guy Pearce.
"I had this notion of just a bullet getting sucked out of the wall and into the barrel of a gun," he told Complex, explaining the inspiration behind his use of time inversion in the opening scenes of the 2000 movie.
"It's an image that I had in Memento to demonstrate the structure of that movie, but I always harboured this ambition to make a film where the characters had to deal with the physical reality of that.
"In a way, an idea comes to the fore when the time is right for it, and it's a hard process to quantify, so I was doing all these other things. There are things that you learn how to make and everything in Tenet, interestingly, on the surface of it, they're all versions of action or particular ways of filming things that I've tried before in a different form. You're building on what you've done in the past."
