I’ve always felt that a key part of writing was establishing what is and isn’t possible in the story. Yeah, it’s fiction—anything’s possible, but there have to be some parameters. Is my story set in the real world? Something close to the real world? Something completely unlike the world as we know it?
It’s important for a writer to know these things because it’s easy for the reader to feel cheated when a story reveals elements that don’t fit in the established world. Imagine the outrage if, in book seven of A Song of Fire and Ice, we learned that Tyrion wasn’t a dwarf but an exiled alien prince inserted into the Lannister family via hypnotic ray. Or if on iZombie we learned that Liv became one of the undead because of a secret voodoo ritual, not a chemical mixture. When we go through a classic locked-room mystery novel and discover, ten pages from the end, that the killer’s a vampire who turned to mist and slipped through the keyhole… that’s frustrating and annoying.