Giles: "Your predecessor was the Slayer for 12 minutes. She prevented the apocalypse. I dare you to do better. Enlist at the Watchers Academy"
Buffy: "Seriously, with the talking to me? Not exactly getting the why."
Xander: I suffer from aviophobia. It means fear of dying in something that flies!
Giles: The purpose is to experience fear, fear in the face of certain death, to accept that fear, and maintain control of oneself and one's Scoobies, this is the quality expected in every Slayer.