You see, evil always contains the seeds of its own destruction, it is ultimately negative, and therefore encompasses its downfall even at its moments of its apparent triumph. No matter how grandiose, how well-planned, how apparently foolproof an evil plan, the inherent sinfulness will by definition rebounds upon its instigators. No matter how apparently successful it may seem upon the way, at the end it will wreck itself. It will founder upon the rocks of iniquity and sink headfirst to vanish without trace into the seas of oblivion.
— Aziraphale to Crowley, Good Omens by Neil Gaiman and Terry Pratchett
Mermaid-In-Training 