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 GuinSci-fi uses the images that sf - starting with H.G. Wells - made familiar: space travel, aliens, galactic wars and federations, time machines, et cetera, taking them literally, not caring if they are possible or even plausible. It has no interest in or relation to real science or technology. It's fantasy in space suits. Spectacle. Wizards with lasers. Kids with ray guns. I've written both, but I have to say I respect science fiction enough that I wince when people call it sci-fi.
Ursula K. Le Guin