You are standing on a beach.
The sand is coarse, the waves are periodic, the sun is intermittent and the horizon is concave. You face the water. You take a step forwards, towards the water. The water retreats away from you. You take another step forwards, towards the water. The water retreats. You take two steps forwards, towards the water. The water retreats and retreats.
Facing the water, you increase your pace and take three steps forwards, towards the water. The water retreats, matching your pace.
The distance between you and the water is the same as it was seven steps ago.
You are now standing on sand that was underwater seven steps ago. It’s dry. You look left. A line slowly forms between the water–sand divide, which gains definition as it arcs to the right, until it caresses the concave horizon and becomes indistinguishable from it. The horizon is interrupted by protruding peaks of sand dunes that look unclimbable. You look right. A line slowly forms between the water–sand divide, which gains definition as it arcs to the left, until it is caressed by the concave horizon and becomes indistinguishable from it. The horizon is interrupted by protruding peaks of sand dunes that look unclimbable. You look straight, facing the water. The sand is coarse, the waves are periodic, the sun is intermittent and the horizon is concave.
You turn around and face the sand dunes, turning your back to the water.
You take a step forwards, towards the sand dunes. You turn your head and see the water advance towards you. You take another step forwards, towards the sand dunes. You turn your head and see the water advance. You take three steps forwards, towards the sand dunes. You turn your head and see the water advance, matching your pace.
You turn around and face the water.
You run forwards, towards the water. The water retreats, matching your pace.
The distance between you and the water is the same as it was when you last checked.