DUMB: Zuckerberg's first investor was Harvard classmate Eduardo Saverin, who was lazy and not a good worker

What happened: Back in 2003, Zuckerberg realized he needed money to pay for servers for some of the Web projects he was working on while a student at Harvard.

He had a rich friend named Eduardo, and he asked him to help.

Eduardo wanted real responsibility, and Zuckerberg gave it to him. Big mistake. During the summer when Facebook really took off, Eduardo was back in New York partying. He even used Facebook ad space to advertise his own startup. Zuckerberg ended up diluting his shares in an effort to push him out of the company. Eventually Saverin sued and got a big $5 billion settlement.

What could have happened: Pushing Saverin out of the company like that could have resulted in a disastrous lawsuit that Zuckerberg – who borrowed $85,000 from his parents to keep Facebook running that summer – could not have afforded. Zuckerberg got lucky that Saverin wasn't paying attention.