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.
Frederik PohlWhen I sit down to the feast of life ... I'm so busy planning on how to pick up the check, and wondering what the other people think of me for paying it, and wondering if I have enough money in my pocket to pay the bill, that I don't get around to eating.
Frederik PohlIf you don't care about science enough to be interested in it on its own, you shouldn't try to write hard science fiction. You can write like Ray Bradbury and Harlan Ellison as much as you want.
Frederik Pohl