“Needless were none of the deeds of Gandalf in life. We do not yet know his full purpose.”

Little bit of Tolkien for you there. As writers, throughout our lives we commit deeds to paper, but the best of us will use deeds that are needless. I doubt my grammar in that sentence but the point still stands. I call them characterisers. They flesh out characters. Maybe you give a character a relationship with someone utterly unconnected to the plot, or you introduce how the character owns a gun, even though it’s never used. It all adds up to a better experience for the reader. Your challenge is not to flesh out characters. No, it’s something much harder.

You have to create an unnecessary story. A story that has no purpose. Something needless. How you do it is up to you. Maybe you write about Hermione’s breakfast on a day that nothing happened or you write about your fictional sibling’s birthday. Your choice. But it has to bear no relevance to anything. Ask me for more explanation in comments, I’m low on chars.