So does the annual event National Novel Writing Month.
It turns out that I'm addicted to this challenge. You would think have several novels that need editing would be enough for me. But no, I can't resist the call of NaNoWriMo.
Some years, I do little prep at all. I go into the challenge with one or more main characters in my head. A basic idea of what the story should be but little more than that.
In 2012, I had a story line that I'd been posting to tumblr that I decided was part of a much bigger story. So that year, I had some of the world worked out and a clearer picture of the main character than usual.
This year is similar. Earlier in the year, I wrote a short story "The Gladiator". A couple of people remarked that they were interested in what happens next. Expanding this to a novel gives me the opportunity to better develop the back stories of the characters and then send them off to change the world. So, I have characters and I know how the first part of the story goes.