Why didn’t the farmer know what to do when the sack of wheat fell on the ground?

Once upon a time a poor farmer taking a sack of wheat to the mill did not know what to do when it slipped from his horse and fell on the ground. The sack was too heavy for him to lift, and his only hope was that presently someone would come riding by and lend a hand. It was not long before a rider appeared, but the farmer’s heart sank when he recognized him, for it was the great man who lived in a castle nearby. The farmer would have dared to ask another farmer for help, or any poor man who might have come along the road, but he could not beg a favor of so great a man. However, as soon as the great man came up he got off his horse, saying, "I see you’ve had a bad luck, friend. How good it is that I am here just at the right time!" Then he took one end of the sack, the farmer the other, and between them they lifted it on the horse.  "Sir," asked the farmer, "how can I pay you?" "Easily enough," the great man replied. "Whenever you see anyone else in trouble, do the same for him."