One of the greatest Asimov's short novels I had the pleasure of reading. Can you imagine what happenned to us if we've at night, and in one entire continnent, the electricity were ran out !? And what in one entire planet. It is true, being us, humans, able, as species that lives under the light of the Sun, were able to conquer the Night after the invention of the electric lamp, but what can happend if those things where gone suddenly !? This way, you can start to feel how the inhabitants of this planet suddenly fallen into darkness would start to feel. The Mayans believed that one day the Sun would not rise anymore. It could not have been the end the Day, but the end of one entire civilization. The Night can come in different ways, it doesn't need to be the necessarily by the means of the sun disappearing below the horizon.