The Deer Herd's Sleeping Watchman

A herd of deer, grazing regularly in an open meadow bordered by dense forest where hunters sometimes lurked, had established a simple system for safety: one deer would take a turn each day standing watch on a small rise while the rest grazed with their heads down, trusting the watcher to alert them at the first sign of danger.

One afternoon, the deer assigned to watch duty, having watched uneventfully for many days in a row without incident, grew drowsy in the warm sun and drifted into a light doze while still standing at his post, never intending to fall asleep but unable to resist the day's heat and his own accumulated boredom from days of nothing happening.

Hunters approached during exactly this lapse, and only the herd's own scattered luck — a sudden gust of wind carrying their scent early, a snapping twig underfoot — saved them from disaster that the sleeping watchman never once warned them about. Furious but more troubled than angry, the herd's elders instituted a new practice afterward: the watcher would be required to call out a simple signal at regular, timed intervals throughout his watch, not just when danger appeared, so the herd could tell the difference between an alert watcher and a merely present one before it cost them everything. Trusting that a duty is being done, they realized, is not the same as actually verifying it.