Terry Pratchett (wildly successful author of the Discworld series) once quipped that fantasy is just scifi without the nuts and bolts. I take that as indicating that fantansy and scifi are related in that they both create narratives around fictional mechanics. The tropes differ, but they are exploring the similar space of what might happen in a world with mechanics (e.g. magic, 'quantum') allowing completely different set of experiences than the real world.
Just google his name and "rivets". Looks like it's actually a joking remark Card makes himself to express what it's like to dabble in both sci-fi and fantasy (Card is successful with both).
Card maintains that switching genres wasn't a difficult
thing for him. He believes that, ultimately, the
difference between the two genres is largely on the
surface. "Half joking, I was writing to Ben (Bova) about
this very subject, and I said, look, fantasy has trees,
and science fiction has rivets. That's it, that's all
the difference there is, the difference of feel,
perception.
