Remember Aesop's fable "The Lion and the Mouse"? The one where a huge lion catches a tiny mouse and is ready to swallow him but the mouse very convincingly pleads for his life.
The mouse says (I'm paraphrasing...), "Please let me go. You never know when I might be able to help you one day, and I will." Amused at the thought of the tiny mouse ever being able to help him, the lion lets him go.