But you must not change one thing, one pebble, one grain of sand, until you know what good and evil will follow on that act. The world is in balance, in Equilibrium. A wizard's power of Changing and Summoning can shake the balance of the world. It is dangerous, that power...It must follow knowledge, and serve need.
Ursula K. Le Guin, A Wizard of Earthsea
equilibrium, mage, magic, wizard