"Ambition is key because he[Bill Gates] could have left Microsoft much earlier, and moved on to do anything else he wanted as extremely wealthy man. He was already a billionaire when he chose to stay, and turned Microsoft into an empire."

Value creates opportunity.

I'm not suggesting that Bill Gates wasn't/isn't ambitious, but if one of your ventures has made you a billionaire I'd imagine it be much easier to stay on board and see how far you can ride that train.