In 2006, when CEO Mark Zuckerberg was just 23, Yahoo offered a billion dollars to buy Facebook. After some consideration, Mark turned them down.
Having made that decision, as Mark explained in a BBC documentary shown at the weekend, it was then easier to reject an offer the following year from Microsoft to buy the company for $15 billion (nearly a quarter of which would have gone to Mark himself).
Think about that for a moment: turning down $3.6 billion. Was he not tempted to take the money? Wouldn't you be?
Mark may have believed the company would later be worth more (and indeed it is) but that wasn't the primary reason he refused to sell. His reason was that, as he explained, "The thing I really care about is the mission, making the world open."
He's one of the youngest billionaires in the world but he is obviously not in it for the money. He wears the same clothes, drives not a ferrari but an executive's car, and sits in an open plan office with the rest of his employees.
Mark works long hours at Facebook. And when he gets home he continues talking to his employees within the Facebook site. And yet he loves it. When he has freely chosen this path, he loves what he does, and he's not doing it for the money, is it work or play?
Stories like Mark's raise a question for the rest of us:
What, if anything, would you be willing to work (or play) hard enough on to make a billion dollars?
But it also raises a far more interesting question to consider and it's this:
What do you care enough about to turn down a billion dollars so you can keep doing it?
I suspect that the people who can answer this question are the ones most likely to make that billion.
What could it be for you?