Sam crossed three hills, each more difficult to climb than the last. He sensed that the fatigue he felt was due to more than the walking. By the time he reached the base of the fourth hill, he was almost exhausted. It was as though he’d been running for several kilometers, but he remembered only having walked along the road. Somehow he knew that: more than a walk through the countryside had happened, but he had no memory of it. Determined to persevere, he started up the next hill.