A farmer had a donkey which he used to carry various goods to and from the market in town. One day, the farmer bought several bags of salt, loaded them on the donkey, and headed for home. As they were crossing a stream on the way to the farm, the donkey slipped and fell,
and much of the salt in the bags was dissolved away in the flowing water. When the Donkey finally got up out of the stream and began walking again, he noticed, much to his delight, that his load had become much lighter.
A few days later, the farmer and the donkey once again went to town, this time for sugar. The bags of sugar were loaded on the donkey's back, and the two of them began to make their way toward the farm. As they approached the stream, the donkey remembered what had happened with the bags of salt, and when he was in the middle of the stream, he deliberately stumbled and fell. Once out of the water, the donkey was quite pleased to find that his load was once again a great deal less burdensome.
This continued to happen each time the farmer and the donkey made a trip to town, and the farmer soon guessed the cause of his donkey's newly acquired clumsiness. The next time they went to market, the farmer bought a load of sponges. The donkey was very happy to discover how light this load was, to begin with and looked forward to its being almost as nothing after they crossed the stream. When he fell into the water this time, however, the sponges soaked it up and became much, much more massive than they had been at first. The donkey struggled slowly back to the farm under the massive load, and after that became very surefooted indeed. The farmer never had to worry about the donkey falling into the stream again.
-- a fable from Aesop, rendered here by Peter Theodore