Mark Zuckerberg has led Facebook to become one of the most valuable and respected companies in the world. But despite all of his successes, he rarely talks about the challenges he's faced along the way.

In a new interview with Y Combinator president Sam Altman, published on Tuesday, Zuckerberg showed a more vulnerable side when he discussed some of the low points in Facebook's early history, as well as some of his failings.

"One of the hardest parts for me was when Yahoo offered to buy the company for a lot of money," Zuckerberg said. "That was the turning point in the company."

That was 2006. Facebook (FB) was about 2-years-old and had 10 million users. Yahoo (YAHOF) wanted the company for $1 billion.

Although a lot of people believed Facebook should take the offer, Zuckerberg said he and co-founder Dustin Moskovitz ultimately decided to keep growing the business on their own terms.

"The part that was painful wasn't turning down the offer," he said. "It was the fact that after that, huge amounts of the company quit because they didn't believe in what we were doing."

Facebook's whole management team was gone within a year.

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Zuckerberg placed the blame on himself for the exodus.

"I think the fact that I didn't communicate very well about what we were trying to do caused this huge tension," he said. "A lot of folks who joined early on... weren't really aligned with me. ... Being able to sell a [startup] for $1 billion after a couple of years -- that was like a home run [for them]...."

During the 25-minute video interview, Altman also prompted Zuckerberg to explain how Facebook decides which products to test and build.

The Facebook CEO highlighted how it uses a combination of a scientific method -- testing different hypotheses -- and user feedback and data analysis, but added that it wasn't always enough. Facebook's $2 billion acquisition of Oculus in 2014 is proof.

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"I actually view that as -- if we'd done a better job of building up some of the expertise to do some of that stuff internally then maybe we wouldn't have had to do that," said Zuckerberg. "We bought the Oculus team for a lot of money ... as CEO, it's your job to not get in a position where you need to be doing these crazy things."

But he conceded that over the course of time, big bets like this will have to be made.

"It's inevitable," said Zuckerberg. "You can't be ahead of everything."