"The Sea and Little Fishes" is a short story by Terry Pratchett, written in 1998. It is set in his Discworld universe, and features Lancre witches Granny Weatherwax and Nanny Ogg.
The story established a basis for various elements of the novel A Hat Full of Sky, but is not required to understand that novel.
A coalition of witches, led by self-appointed organiser Lettice Earwig, asks Granny Weatherwax not to participate in the annual Lancre Witch Trials, on account of her always winning. She agrees, becoming disconcertingly nice. This is because Granny has made it clear in the Tiffany Aching series that she does not approve of Lettice Earwig's methods, and admitting that a rival is correct at the time of her own choosing is the greatest and most calculated insult Granny can possibly deliver to another witch, essentially having agreed with Lettice Earwig's own unwitting 'admission' that she cannot beat Granny.