The day Dustin Moskovitz decided to tell his co-founder Mark Zuckerberg he was leaving Facebook, he prepared a speech, asked for some one on one time and then told his Harvard buddy it was time to move on.

Moskovitz, who revealed the story in a candid chat with Sarah Lacy at tonight’s PandoMonthly in San Francisco, said there was no easy way to get the message across.

“Were you nervous?” Lacy asked.

“Yeah, of course,” Moskvitz replied. “That was certainly one of the hardest things I’ve ever done.”

Zuckerberg was disappointed, but he took it well and said he would support Moskovitz in his next step, the 27-year-old billionaire said.

Moskovitz decided to leave Facebook to start enterprise software company Asana, which he founded with former Facebooker and Google engineer Justin Rosenstein. He didn’t feel like Facebook’s mission had been completely carried out, but at the time he had been consumed with working on an internal communications tool for the company. He ultimately decided his work on the tool represented mission creep, so he decided to head off in a new direction.

Moskovitz also discussed 2006′s $1 billion Yahoo acquisition offer, which Facebook famously turned down. He estimated that 70 to 80 percent of the company’s management disagreed with him and Zuckerberg, who didn’t want to sell the company.

“So,” asked Lacy, “there was not a moment of hesitation of, ‘Shit, that’s a billion dollars – we should take this?’”

After a few beats of hesitant silence – punctuated by laughter from the crowd of 400 – Moskovitz eventually said for him and Zuckerberg, it wasn’t about the money. “It was about making that product and making it big, and we spent a long time thinking about: Can we do that better at Yahoo?”

Yahoo’s corporate strength was a little more ambiguous back then, Moskovitz pointed out. Ultimately, however, he and Zuckerberg didn’t like Facebook’s prospects, if the sale went through.

The clincher? “The track record of companies doing better after being acquired,” he said, “is basically non-existent.”