Leonard Cyril Deighton (/ˈdeɪtən/; born 18 February 1929) is a British author. His publications have included cookery books and works on history, but he is best known for his spy novels. (wikipedia)
Anyone can write one book: even politicians do it. Starting a second book reveals an intention to be a professional writer.
In Mexico an air conditioner is called a politician because it makes a lot of noise but doesn't work very well.
I wrote my first books the way people would write science fiction, because they gave me much more latitude to invent situations.