My first run was bad. Training between runs was bad. Waiting (for other competitors to finish) was the most nervous I've ever been in my life. I skied a slow, conservative run, but it was solid. It was really clean, and I think that's what won it for me.
On the actual competition days, you get about three or four hours of physical exertion - between an hour-long warm-up, recovery in-between runs, the training runs, and then the runs themselves.