The Donkey Who Learned to Fall

A donkey, loaded with heavy sacks of salt for a merchant's journey across a river, stumbled and fell while crossing a ford one day, submerging his entire load beneath the water for several long moments before his owner managed to help him back up. To his considerable relief, he found the load felt dramatically lighter once he stood again, the salt having dissolved substantially into the river during his fall.

Delighted with this unexpected discovery, the donkey began deliberately stumbling and falling into the water at every subsequent river crossing, quickly learning that a well-timed tumble reliably lightened whatever heavy load he happened to be carrying that day, sparing his back considerable strain for the rest of each journey.

His owner, growing increasingly suspicious of the donkey's suspiciously frequent and consistent "accidents" always occurring at exactly the deepest part of every crossing, eventually caught on to the pattern and devised a clever countermeasure: on the donkey's next journey, he loaded him instead with sponges rather than salt, appearing similar in weight and shape from the outside. The donkey, following his now well-practiced trick, deliberately tumbled into the river as usual — only to discover the sponges soaked up enormous amounts of water and became far heavier than before, forcing him to struggle to his feet under a crushing new burden entirely of his own making. He never attempted the trick again, having learned that a clever pattern, once someone else recognizes it, can easily be turned into a trap of your own design.