Even the brightest sun can be obscured by a dark cloud, or fall behind a mountain, or slip beneath a sea. This is the harmony of nature. Each thing taking its turn, one no stronger than the other. Light is overcome by darkness which then is overcome by light once again. It is unceasing. The cycle goes around and around until it comes full circle once more. Tides come and go under the watchful eye of the moon and order is maintained by the universe.