Maybe Daniel isn't "persevering against crazy odds" and "willing himself to success". It's apparent from the story that he's a really fucking good coder. With a reasonably accurate estimation of his own abilities, and with all the support and inspiration around him at YC, it didn't take much perseverance and extraordinary will to put something together. He just had to continue doing what he loves and does best... writing code.
I certainly can't speak for Daniel. I get tired of these descriptions of entrepreneurs that make them sound like cancer survivors. I think founders often have extraordinary skill, and that changes the required personal characteristics considerably.