A fundamental force on the Discworld: the power of story itself. On the Disc, things tend to happen because that's how stories go - the million-to-one chance always comes through (but only if it's exactly a million to one), the heir to the throne will always be found, and the plucky hero will defeat the dark lord. Pratchett uses narrative causality both as a plot device and as a tool for examining how stories shape our expectations and behaviour in the real world.