Just came across this quote from Ursula Le Guin's A Wizard Of Earthsea, which reminds me of the book on Zen Buddhism I'm currently dipping into.
"You thought, my boy, that a mage is one who can do anything. So I thought, once. So did we all. And the truth is that as a man's real power grows and his knowledge widens, ever the way he can follow grows narrower: until at last he chooses nothing, but does only and wholly what he must do."