The first run of our game is now ober half way through. While building the set was a lot of work, running the game isn't walk in the park either. Evan though we have tried to prepare for everything there is always something missed or that go wrong.
While we could prepare as much as possible when it gomes regarding the setting and main plot in the end it comes down to the players. While there are main script and characters are well designed it's still up to players to decide what they choose to do. It's a co-creation after all - players have the power to affect the game as much as we do. After all, it's not a play where every line the characters say is prewritten.
And that's the joy of running these games. Even though you know the story and in some level what's going to happen it's still a completely different, new story every time.