I think that when Locke was shot and laying there in the death pit, He believed that it was the end and thought he'd just shoot himself and be put out of his misery, and he Believed he couldn't move - paralyzed again,, but then when he saw Walt and started to believe again, he then could get up and walk. It was all in his own belief - in his own power. and then he made the Skeleton ladder and climbed out!!!