Walter Isaacson, who spent two years shadowing the mercurial billionaire for a new biography, noted on the Lex Fridman Podcast that at the beginning of last year, Musk “was riding high,” with sales roaring at Tesla and launches getting routine at SpaceX.

“And yet he’d said, ‘You know, I still want to put all my chips back on the table. I want to keep taking risks. I don’t want to savor things,’” Isaacson recalled. “He doesn’t like to coast.”

That attitude helps explain why Musk started secretly buying shares of Twitter early last year and—after a monthslong legal drama—fully acquired the company in October.

But why bother taking over Twitter at all—and risk getting mired in controversy and legal scuffles—when things were going so well at Tesla and SpaceX? 

“Elon Musk is cut to be an executive in a highly intense situation, so much so that when things get less intense—when they actually are making enough cars and rockets are going up and landing—he thinks of something else so he can surge and have more intensity. He’s addicted to intensity,” said Isaacson.

Marc Andreessen, general partner at venture capital firm Andreessen Horowitz, brought up Musk this month while speaking on the Huberman Lab podcast. Discussing the personality traits of disruptive entrepreneurs, he said, “There is this decision that people have to make, which is, ‘Okay, if I have the latent capability to do this…do I want to go through the stress and the pain and the trauma and the anxiety and the risk of failure?’” 

Musk, he said, is a rare individual “who just can’t do it any other way… That’s why he’s running five companies at the same time and working on a sixth.” 

For the biography, venture capitalist Peter Thiel told Isaacson that Musk was addicted to the thrill of risk. Speaking of Tesla and SpaceX, he said, “Silicon Valley wisdom would be that these were both incredibly crazy bets.”

Isaacson described Musk’s addiction to intensity as a “super power,” adding, “There is always a big mission above it. So I would say it’s an empathy towards people in the big picture. It’s an empathy towards humanity more than the empathy towards the three or four humans who might be sitting in the conference room with you.”

He said in that regard Musk has traits similar to other disruptive entrepreneurs, such as Microsoft founder Bill Gates: “They always have empathy for these great goals of humanity, and at times they can be clueless about the emotions of the people in front of them, or callous sometimes.” 

Gates, it’s worth noting, also spoke to Isaacson for the biography, saying that Musk became “super mean to me” after learning he had shorted Tesla’s stock, or bet that it would decline in value. “But he’s super mean to so many people,” he added, “so you can’t take it too personally.”