Some people assume that authors write books because we have vivid imaginations and want to share our vision. Other people assume that authors write because we are bursting with stories, and therefore must scribble those stories down in moments of creative propondidty.
Both groups are completely wrong. Authors write books for one, and only one, reason: because we like to torture people.
Take for instance, the word I used above. Propondidty. There is no such word — I made it up. Why? Because it amused me to think of thousands of readers looking up a nonsense word in their dictionaries.