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 GuinNow they came back to him, on this night he was seventeen years old. All the years and places of his brief broken life came within mind's reach and made a whole again. He knew once more, at last, after this long, bitter, waisted time, who he was and where he was. But where he must go in the years to come, that he could not see; and he feared to see it.
Ursula K. Le Guin