The Facebook cofounder delved into his views on optimism—and just as important, pessimism—on a Monday episode of the Huberman Lab podcast.

One of his favorite sayings, he explained, is that “optimists tend to be successful and pessimists tend to be right.” 

He continued: “I do think that there’s really something to it…If you’re discussing any idea, there’s all these reasons why it might not work. And those reasons are probably true. The people who are stating them probably have some validity…But the question is, is that the most productive way to view the world? Across the board, I think the people who tend to be the most productive and get the most done—you kind of need to be optimistic, because if you don’t believe that something can get done, then why would you go work on it?”

Zuckerberg, who considers himself an optimist, certainly believed that Facebook, which he cofounded nearly 20 years ago, would catch on. But he also heard plenty of criticism from doubters who couldn’t imagine it taking off. Among the doubters was investor Andrew Chen, currently a partner at venture capital firm Andreessen Horowitz. Chen met the Facebook team when it consisted of about 12 people. He wasn’t very impressed and passed on what would have been a blockbuster investment. 

“They didn’t know much about advertising,” Chen later wrote. “Their monetization strategy seemed superficial at best.” The idea that Facebook would one day be bigger than portals like Yahoo, MSN, and AOL “never crossed my mind,” he added, admitting to his “failure to understand Facebook’s potential.”

Zuckerberg, of course, remained optimistic—and the rest is history.

He’s remained similarly optimistic about the potential of the metaverse, despite investors getting nervous about Meta spending tens of billions on the project with little to show for it. “Those who are patient and invest with us will end up being rewarded,” he insisted on an analyst call last year.

He’s been consistently upbeat about the potential of artificial intelligence to improve people’s lives, as well, whereas Tesla CEO Elon Musk has described AI as a “fundamental risk to the existence of human civilization.” 

“With AI especially, I am really optimistic,” Zuckerberg said in a Facebook livestream in 2017. “And I think people who are naysayers and try to drum up these doomsday scenarios—I just, I don’t understand it. It’s really negative, and in some ways I actually think it is pretty irresponsible. In the next five to 10 years, AI is going to deliver so many improvements in the quality of our lives.” 

Of course, many would argue Zuckerberg has been too optimistic in some regards, with Facebook in many eyes becoming a cesspool of disinformation and conspiracies. The company has repeatedly been accused of privacy violations, including during the Cambridge Analytica scandal. Being a bit more pessimistic could have saved Zuckerberg a lot of trouble, it would seem. 

That said, he is not one to filter out criticism. “If you tune out everyone who thinks that you’re not doing something right, then you’re going to miss a lot of really valuable signals to do stuff better than you’re doing it today,” he told The Verge last year.

Also on the podcast was Zuckerberg’s wife, Dr. Priscilla Chan, with whom he cofounded the Chan Zuckerberg Initiative. The organization, fittingly, has the optimistic goal to cure all human diseases by the end of this century, with a focus on funding projects at the intersections of biology, engineering, and AI. 

“I will say that we are incredibly hopeful people,” said Chan. “But it manifests in different ways between the two of us.”

Zuckerberg suggested he was more “technologically optimistic about what can be built,” while for Chan as a doctor it was more about “being able to improve the lives of individuals.”

Chan agreed with that, but also described one downside of her husband’s optimism in day-to-day life:

“As life partners, our relative optimism comes through as, Mark just is overly optimistic about his time management and will get engrossed in interesting ideas. And he’s late. I have to channel ‘Mark is an optimist’ whenever I’m waiting for him…His optimism translates to some tardiness.”