The Nail
This is a classic fable attributed to the Brothers Grimm that illustrates the principle of unintended consequences through a simple narrative of negligence. A merchant's impatience to reach home before nightfall leads him to ignore repeated warnings about a missing nail in his horse's shoe, resulting in the horse's injury and his own misfortune. The story serves as a timeless moral lesson about the importance of attending to small problems before they become catastrophic.