Just the excitement to see it done, for the sake of it. I think money won't even remotely come to mind.

For the second point on persistence, this guy must have a lot of patience. I've struggled on this actually. If the initial push is strong enough I sit through 3-4 days but at least for me I can't seem to come back and finish it if I put it away for more than a day.

Truly impressive considering all this.