Paul Sakuma, Associated Press
Facebook CEO Mark Zuckerberg poses at his office in Palo Alto, Calif. Joe Green could have worked with Zuckerberg at Facebook but declined, possibly loosing out on a $3 billion payday.

People don't always know the repercussions of a decision, but Joe Green figures his decision lost him $3 billion, according to Business Insider.

Green, a roommate to Facebook founder Mark Zuckerberg at Harvard, was asked to run the business side of Facebook when it began. Taking the offer would have given him 4 or 6 percent of the company, Green told Business Insider.

But Green listened to advice from his father, a professor at UCLA, who recommended he not go into business further with Zuckerberg. Previously, Green and Zuckerberg got into trouble with the university after creating Face Mash, according to the article.

However, Green was still able to earn some Facebook stock for being an adviser to the company and as a cofounder of the Causes and NationBuilder companies.

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