As time passed she grew into an adult dog. What she didn't know was that the chain's corkscrew mount into the ground was not very strong. It held her as a puppy, but now that she was 75 pounds and a strong adult dog, she could easily break free if she risked running hard at the perimeter. But she never even considered doing that. It was not part of her reality.
Confronting the edge of one's reality was clearly depicted in at the end of The Truman Show- another awesome movie by Peter Weir (see clip).
Are there things in our life we could easily free ourselves from, but do not challenge due to experiences from the past? The I Ching (Wilhelm/Baynes translation) describes this as, "A man (or woman) is oppressed by bonds that can be easily broken."
So maybe its time to make a run at our flimsy constraint. We could break through our contrived movie set. We could challenge the parameters of our existence. Who knows, there may be a whole new world waiting for us on the other side.