The former Monty Python legend was J.K. Rowling's first choice to helm Harry Potter and the Philosopher's Stone in 2000, but Warner Bros. studios decided to go with Chris Columbus.
At the time, Gilliam was furious - denouncing Columbus' work as "terrible" and "pedestrian".
But looking back, the 12 Monkeys moviemaker is glad he was overlooked - insisting he couldn't have handled studio bosses meddling with his work over revenue fears.
He tells Total Film magazine, "That was one of my lucky moments. I would have gone crazy. It's a f**king factory, working on Harry Potter. It is. The studios are staking everything on the success of those movies.
"It was way too expensive. Too much at stake. So they (studio bosses) interfere. It's about serving something higher than yourself. It's the film. The film is God and I'm worshipping... while I'm making it I become a zealot. Basically, I'm a like a suicide bomber when it comes to my films!"