used to describe something impossible to happen since Fairy tale that written rarely have sad ending
see example 1
in addition it may used as act of envy by certain people to envy the persons that live in happiness and joy like fairy tale
see example 2
Example 2: if Cinderella dies I will be the happiest girl in the world and her husband will be mine .
Origins * : it comes from Cinderella's step mother and sisters
*if Cinderella dies you will only the ones who is for Prince Charming .