Do you know Aesop's fable The Lion and the Mouse?
It's the story of how a lion catches a mouse. The mouse says that one day it will help the lion, so the lion decides to let the mouse go free instead of killing it.
Later, the mouse is able to help set the lion free from a hunter's trap.
The moral of the story is that a kindness is never wasted. Do you agree? Have you ever helped someone who then helped you?