Andy Weir has done pretty well when it comes to adaptations. His first novel, The Martian, was turned into a movie in 2015, and the Ridley Scott-directed picture earned more than $600 million at the box office. And Project Hail Mary just had a huge opening weekend that puts it on track to be one of the year’s biggest movies. However, despite that success, Weir tells me that he does his best to keep the idea of an adaptation out of his mind when he starts a new novel. “I try not to think about it at all,” he explains.

The reason, according to Weir, is that the two mediums are just so different. That’s something he’s learned over the last decade, particularly when it comes to Project Hail Mary, which Weir served as a producer on. “I was intimately involved in every aspect of the production,” he explains. “I was there for the shoot, principal photography, I was involved in casting and picking directors, post-production and editing. I got to give notes on everything. The main reason that I’m a producer is because of the way that my contract is structured, but for the most part I tried to stay out of the way of the real producers who knew what they were doing.”

That role gave him more insight into how films are made — on The Martian, he says, “they just gave me money and told me to go away” — but he says that his experience with both movies hasn’t changed how he approaches his writing process.

Here’s how he explained it to me:

When I’m writing a book — and this is advice I give to all authors — I don’t think about a movie adaptation. If you want to write a movie, write a screenplay. But if you want to write a book, write a book. And you should be focused on the reader’s experience while they’re reading your book. You shouldn’t be limiting yourself by what would make a good cinematic movie. You need to be focused on what makes a good literary book. Because there are a lot of things you can do in books that you can’t do in movies, and vice versa, so you should take advantage of your much larger canvas and the flexibility you have with the written word. Just use all of those tools rather than limiting yourself to basically writing a novelization of a movie that you have in your head.

“He’s got these wonderful big, cinematic ideas,” Goddard says. “He has a wonderful sense of plot. For me personally, it’s the soul of his writing that really makes it transcend. It’s easy to overlook because his ideas were so big, and the hard science is so front and center, I think people think that that is the key to his success. But for me, I like that he’s writing about these deeper themes about humanity. He would say he’s not, he’s just trying to give you a good time. I don’t agree with him. I see these beautiful themes of human compassion and emotion that are in between the words that he is writing, and I feel like my job is to bring that soul out and put that soul on the screen.”

And that’s what helped Goddard get over that initial fear when it came to Project Hail Mary’s script. “I knew that we have to try because I love this book so much,” he says.