...the tricky thing about imaginative fiction, both science fiction and fantasy, is the coherence of the imagination, because you are making a whole world out of words only. It's all made to hold together."
That's what fiction does, isn't it? All fiction? It makes a world and makes it seem real. Inner coherence (which can become aesthetic completeness) is the principle secret. It's achieved by imagination, selection, and accurate description--whether any counterpart to it exists in the real world or not really doesn't matter.
What does matter, perhaps, is whether we can find ourselves in the story as we
read it, can recognize the emotional and moral weight of human existence. Sf and fantasy are not as relentlessly human-centered as realistic fiction; they both show human beings in relation to the nonhuman, they include the human subject in a larger or stranger universe than the realistic novel does. But the story is still about us. We seem to be all we are ultimately interested in. And so, for writers and readers who see people as individuals rather than as types or groups, character becomes important even in genres where it is usually considered secondary.
What do you think matters?