The future depicted in a good SF story ought to be in fact possible, or at least plausible. That means that the writer should be able to convince the reader (and himself) that the wonders he is describing really can come true... and that gets tricky when you take a good, hard look at the world around you.

They were two lovely choices. One of them meant giving up every chance of a decent life forever...and the other one scared me out of my mind.

Science fiction is the very literature of change.

A good science fiction story should be able to predict not the automobile but the traffic jam.

You can't really predict the future. All you can do is invent it.

What were we doing here? Traveling hundreds or thousands of light-years, to break our hearts?

It's clear that science and science fiction have overlapping populations.