THE LION AND THE MOUSE 
A mouse happened to run into the mouth of a sleeping lion, who roused himself, caught him, and was just about eating him, when the little fellow begged him to let him go, saying, "If I am saved, I shall be everlastingly grateful." So, with a smile, the lion let him off. It befell him not long after to be saved by the mouse's gratitude, for when he was caught by some hunters and bound by ropes to a tree, the mouse, hearing his roaring groans, came and gnawed the ropes, and set him free, saying, "You laughed at me once, as if you could receive no return from me, but now, you see, it is you who have to be grateful to me."
The story shows that there come sudden changes of affairs, when the most powerful owe everything to the weakest.