“Be seated,” the Princess instructed, pointing at a low bench.  As soon as Twilight sat, Luna moved beside her, although she remained standing, looking at her cluttered desk rather than Twilight.  “What we are about to teach thee will be very difficult for a pony of thy nature to learn—mayst, perchance, turn out to be impossible.  We are sorry to say that although thou canst learn theory from this tome, thou art quite unlikely to be able to successfully cast any of the spells with just book knowledge.