And from what I see in the comments here, a lot of people are misunderstanding the point.
If Jensen, Thiel, or Levchin fully understood the challenges they'd face to get their companies off the ground, they would never have pursued it. That's not to say they regret the results.
For better or worse, they all persevered, and so it's easy for us to say, well yeah, obviously that was the right move. Because PayPal and Nvidia are obvious slam dunks in retrospect. But none of us have been there, as pioneers of the unproven, and it's the height of arrogance to contradict that.