Imagine attending a football game with no rules. I don’t know about you, but there’s a limit to how excited I could get about watching a bunch of men run around with no particular aim in mind. Really, except for the tight pants, it would be pointless.
What makes the game worth watching is knowing your team has a goal, and knowing there’s an opposing team aiming to stop them from achieving it. That’s what pulls you to the edge of your seat, screaming and pumping your fist in the air.
It’s the same when you read fiction. If the writer hasn’t told you how to keep score, you have no way of knowing whether the characters are drawing nearer or farther from accomplishing their goals, and little reason to care.