Ian Plant:

Imagine you are standing in the middle of a small river, gazing downstream. As you survey the scene, you notice that the water flows around, beneath, and past you on its journey into the distant landscape beyond. Along its way, the water rushes over rocks and small drops and curves and turns around successive bends, but the flow of the river is irresistible—anything caught in its path is swept along, following every twist and turn, perhaps getting caught for a moment on a rock emerging from the river’s surface, but inevitably transported into the distance.