John le Carre

Set your sights high, the higher the better. Expect the most wonderful things to happen, not in the future but right now. Realize that nothing is too good. Allow absolutely nothing to hamper you or hold you up in any way.

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.