Marc Andreessen

I would say my fraternity was nothing but a bunch of farm boys; we weren't really in the whole fraternity scene, but yeah, that's a safe assessment of who I am. I've lived that life, growing up in agriculture and then going off to college and joining a fraternity, livin' that life.

The historical novelist has to consider what has actually happened, while the SF writer is dealing in possibilities, but they are both in the business of imagining a world unlike our own and yet connected to it.