When running AI giant OpenAI becomes too overwhelming, Sam Altman turns to pen and paper—it’s a habit shared by Bill Gates and Richard Branson

However, its complete demise may not happen anytime soon, at least if OpenAI CEO Sam Altman has anything to say about it. Despite being the leader of the company behind productivity-enhancing chatbot ChatGPT, the billionaire remains a staunch believer in writing physical notes. Especially when the going gets tough.

“I think of writing as externalized thinking. I still, if I have a very hard problem, or if I feel a little bit confused about something, have not found anything better to do than to sit down and make myself write it out,” Altman said on the How I Write podcast.

“I’m a big believer of, I take a bunch of notes, and then I clearly rip them out so I can look at multiple pages at the same time, and I can crumple them up and throw them on the floor when I’m done.”

Note-taking is a practice that Altman maintains has helped him become a better thinker while building his $300 billion AI giant—and as well as wanting to crumple the notes up after, he has some more highly specific requirements when it comes to his note-taking habits.

Sam Altman’s note-taking habits

Altman said this week at the Federal Reserve that he keeps his notes private as a way to organize his thoughts—but his process is far from just scribbling. His note-taking practice is rather meticulous, and it centers on having the right supplies. This includes having a pocket-size spiral notebook with a hard front and back and that can lie flat on a table, he told podcast host David Perell. The paper also must feel good to write on.

His pen choice is specific, too: either the Uniball Micro 0.5 mm or the “Muji 0.36 or 0.37 in dark blue ink” (though he may be referring to the Muji 0.38).

Only then can he get to work thinking through tough ideas. Each time he sits down to write, he comes away shocked at the power of this seemingly simple exercise.

“I find it astonishing how much writing just for yourself … helps clarify what you actually think, helps sharpen stuff in a way that for me—and I think for a lot of other people—is somehow impossible to do, just like thinking carefully on a long hike,” he said on the How I Write podcast.

“It’s harder to hide really messy thinking when you have to actually write it down and stare at it.”

And while business leaders may prioritize clear communication first and foremost—Altman said that clear thinking is even more important—and one of the best ways to achieve that is by writing things down.

“Clear communication is very much less important, and very much downstream, of actually clear thinking … Unclear communication is a symptom of unfocused thinking, for the most part.”

Fortune reached out to OpenAI for comment.

The habit shared by billionaires like Bill Gates and Richard Branson 

Sam Altman isn’t alone in his analog approach—his habits are also shared by many fellow billionaires, including Bill Gates and Richard Branson.

The Microsoft cofounder said he believes handwritten notes are key for information processing.

“You won’t catch me in a meeting without a legal pad and pen in hand—and I take tons of notes in the margins while I read,” Gates posted on LinkedIn last year.

Similarly, Branson, the cofounder of Virgin Group, said it’s hard to find him without a way to write down his thoughts.

“I go through dozens of notebooks every year and write down everything that occurs to me each day. Some of the ideas contained inside end up turning into reality, and some don’t—but they are all noteworthy,” he wrote in a 2017 blog post.

“An idea not written down is an idea lost. When inspiration calls, you’ve got to capture it.”

Without note-taking, his companies would not be the same, he added. 

And while he admitted he isn’t opposed to digital notes, what matters most is that some form of note-taking is happening: “It doesn’t matter how you record your notes—as long as you do.”