The Lion and the Deer.
One day, a lion, hungry during a famine, strode upon a young deer. After a short chase, the lion was about to feast when the deer, using his knowledge, said, "Please spare me! I am young and weak! I am nothing but skin and bones! If you let me go, I will grow larger and fatter, and will be a better meal for you!" The lion, thinking of what a good meal that would be, let the deer go.
Some time later, the lion, almost dying of hunger, came upon the same deer, who was now a strong buck, and gave chase. The weak and starving lion was too slow for the strong and swift buck, and soon, the lion finally collapsed. When the lion started sulking and moaning, the buck said, "You should have taken me when I was small and weak. Next time, be grateful for what you have."