Why are sequels to great novels often disappointing? Because they are unnecessary. There are exceptions, of course. Margaret Atwood’s The Testaments won the Booker Prize while in Elizabeth Strout’s Lucy Barton novels we see the protagonist and the world changing in ways that would not have been possible in the first book alone. More often than not, however, sequels are born of a writer’s need to write and not the reader’s need to learn any more about the characters. Many sequels are a sign of one of two things – a writer in a rut or a writer, and often...