This cat Garfield chases a dog called Odie up a tree. Their owner comes out and shouts up to them, "Hey Odie. Dogs can't climb trees!" and Garfield says, "It's amazing what you can achieve when you don't know what you can't do."
Imagine you're on a walk and you get hit by a bus, (heavy going I know.) Unfortunately the collision completely wipes out your memory. You don't know what you are, who you are or where you're from. Lets go so far to say you wouldn't even know what a tree was and you've no way of finding out. You find yourself is some remote part of the countryside and you see the beauty of the Hills for the first time. What are the mountains, what’s the green stuff under your feet. What is it? What does it feel like, smell like?
If you can do this exercise and look at the world completely afresh, or are you and avoid being stuck in your assumptions? That's what scriptwriters have to learn to do.