In many ways, the Appalachian Trail is like a river. It’s true that hikers flow through it in two directions. Nevertheless, the trail is a continuous stream.
A Greek philosopher named Heraclitus said, "In the same river we both step and do not step, we are and are not."
While some people, including Plato, have misquoted or tried to simplify Heraclitus’s meaning to something like, “You can't step into the same river twice,” his words are quite deeper.
The water of any spot on a river is never the same. It is constantly in motion, yet the river is constant in its sameness.
The sameness comes from our memory.