I was working with an elementary principal. One of the school's 3rd grade classes had given him a list of responsibilities they assumed formed his job. He showed me the list and chuckled, until he got to an item that he said made him shudder far more than smile: "You fix everything."
That overwhelming mandate contains a big piece of the truth: almost everything that happens in the school is ultimately the responsibility of the principal. What is equally valid is the reality that one person cannot know everything, be everywhere, prevent all problems, and fix everything.