Martin Lewis Perl

Out of the thousand writers huffing and puffing through movieland, there are scarcely fifty men and women of wit and talent... Yet, in a curious way, there is not much difference between the product of a good writer and a bad one. They both have to toe the same mark.

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.