I think almost all of the best non-fiction that has ever been made comes from the result of somebody who can't stop thinking about a certain topic; a very specific aspect, in some cases, of a certain topic.

And second, they got really good at figuring out what they had to say about it.

43 Folders: 43f Podcast: John Gruber & Merlin Mann's Blogging Panel at SxSW, 2009