Things fall apart; the centre cannot hold -- William Butler Yeats, The Second Coming
Systems tend toward disorder. This is a casual paraphrase of the Second Law of Thermodynamics--the Law of Entropy.
Orson Scott Card's "Alvin Maker" books frame evil as the destructive force, which the world tends toward, like water flowing downhill. Whereas good, the constructive force, must work against the tide.
Things wear out, rocks erode away, the sun cools slowly.
Over a decade ago, I read something that Marilyn Vos Savant wrote. I paraphrase it, thus. Information is not subject to entropy. That which stores the information is subject to entropy--paper decays, your hard drive crashes.
Other than Card's "Alvin Maker," I have not read anything which makes entropy a character in a story. But now I am thinking about it. Right now my ideas are soup. I have to overcome my own entropy to make it into something solid.