I think there are two different questions: Will our protagonist achieve their goal? How will our protagonist achieve their goal? You can be unpredictable by

I think there are two different questions: Will our protagonist achieve their goal? How will our protagonist achieve their goal? You can be unpredictable by not knowing where the story is going, or unpredictable by not knowing how the story will go where it must go. I'm a fan of the latter (lots of genre fiction) because it's like a puzzle. I know Harry's going to thwart Voldemort again this book, but it really looks like there's no way he will, so how the hell is he going to do it?