I have always been a keen writer, and after writing my way through my teens, twenties and thirties, I realised this was probably not just a phase!
The basis of Frankenstein is an experiment that pulls the rug from under its own repeatability. “Never will I create another like yourself,” says the scientist to his “odious handiwork.” The book itself, by the same token, is commonly considered a literary one-off. Mary Shelley, however, was not writing in a vacuum.
Charles Dickens sometimes liked to tease and surprise with his endings. Once, as John Gross provocatively points out, he proceeded from a novel that ends in deep gloom with its hero getting married to another that ends fairly cheerfully with its hero getting killed.