What makes a scifi world seem real?

My husband doesn't like fantasy. When we were dating he always told me he liked his science fiction real, with convincing science and logic holding its strange new worlds together - be they ours or alien planets in the future. So why does he love Game of Thrones? I think it's because the social science is so convincingly portrayed. The history hangs together. The characters act according to their nature, or else reveal their nature convincingly through action.

And what makes me enjoy science f...