It's an old magical principle - it's even filtered down into RPG systems - that magic, while taking a lot of effort, can be 'stored' - in a staff, for example. No doubt a wizard spends a little time each day charging up his staff, although you go blind if you do it too much, of course.
Terry PratchettThey felt, in fact, tremendously bucked-up, which was how Lady Ramkin would almost certainly have put it and which was definitely several letters of the alphabet away from how they normally felt.
Terry PratchettI meant," said Ipslore bitterly, "what is there in this world that truly makes living worthwhile?" Death thought about it. CATS, he said eventually. CATS ARE NICE.
Terry Pratchett