Contact with the enemy...

I've always been a big believer in the phrase, "No plan survives contact with the enemy." It's something I use as a gamemaster when roleplaying, and it's something I use when I'm plotting novels and stories. When I'm working with the characters and trying to decide what their course of action is, I have to take into account the fact that nothing should work as planned.

And why should it?

How often do you plan on something and have it work so smoothly that you don't need to react to variables in...