This is an exercise I'm doing while planning a book I plan to write one day. I tend to get too attached to my characters and have trouble killing them off when necessary, and I'm trying to break myself of that. The idea is that you start with the first event of the story, ask yourself how things can go wrong, write that, and continue on, making an unfortunate chain of incidents. Try to write a story using this method. Go wild, make your characters suffer.