The Man, the Horse, the Ox, and the Dog explained simply

One winter's day, during a severe storm, a Horse, an Ox, and a Dog came and begged for shelter in the house of a Man. He readily admitted them, and, as they were cold and wet, he lit a fire for their comfort: and he put oats before the Horse, and hay before the Ox, while he fed the Dog with the remains of his own dinner. When the storm abated, and they were about to depart, they determined to show their gratitude in the following way. They divided the life of Man among them, and each endowed one part of it with the qualities which were peculiarly his own. The Horse took youth, and hence young men are high-mettled and impatient of restraint; the Ox took middle age, and accordingly men in middle life are steady and hard-working; while the Dog took old age, which is the reason why old men are so often peevish and ill-tempered, and, like dogs, attached chiefly to those who look to their comfort, while they are disposed to snap at those who are unfamiliar or distasteful to them.