Teresa Nielsen Hayden does a fell and cruel deed. She does not tell the story of Sir Gawain and the Green Knight:
Making Light: Introduction to New Magics: The Green Knight gave him the axe and knelt down, baring his neck. Gawain took a deep breath, hefted the axe (it's heavy), took one huge swing, and wham! He cut the Green Knight's head clean off. The head went rolling and skittering across the floor like a bowling ball, bumping into the guests' feet, getting blood all over everything. Then the Green Knight's body stood up from where it was kneeling, walked over to the head, picked it up by the hair, and got back on the horse, holding his head up like a lantern. The head's eyes opened. "See you in a year, Gawain," he said, and rode away.
It's been almost a year since then, getting close to Christmas. That's why Gawain is off in the wilderness, looking for the Green Knight's castle. He knows it wasn't a fair challenge. He figures he's going to die. But he's Sir Gawain, most honorable of knights, and he said he'd do it; so here he is.
This is not a story in which "just anything" can happen. It's a story in which a very few things can happen, and so far only one of them has been magical. By the time Gawain comes riding down that forest path, the story's down to a handful of possible outcomes. Gawain may or may not find the castle. The Green Knight may or may not cut off his head. And Gawain may or may not continue to be the most honorable knight in the world, which for him is the really important part.
And how about us, the invisible readers, standing there watching him ride through the forest? It's time for a test. If I'm right about how fantasy works, you're going to feel a little bit ticked at me for not telling you how the story comes out. There are a lot of different ways a story can mean something to us. Caring how it comes out is one of them.
(I'm not going to tell you. Sorry about that. It's a good story. You'll have to read it for yourself someday.)