"And there's the sign, Ridcully," said the Dean. You have read it, I assume. You know? The sign which says 'Do not, under any circumstances, open this door'?"
  "Of course I've read it," said Ridcully. "Why d'yer think I want it opened?"
  "Er...why?" said the Lecturer in Recent Runes.
  "To see why they wanted it shut, of course."†

† This exchange contains almost all you need to know about human civilization. At least, those bits of it that are now under the sea, fenced off or still smoking.
                -- Hogfather, Terry Pratchett