Some Dreams are Nightmares — James Gunn

These stories share a common concept: man has dreamed for centuries about space flight, about happiness, about immortality. If only I could fly to the moon, he has told himself, if only I could find true happiness, if only I could live forever ... then I would be like a god. These stories, however, go on to demonstrate that every dream come true brings unforeseen consequences. The power of man to dream and make his dreams come true is unlimited, but each step forward must be paid for, there is no such thing as a free lunch, and some dreams are nightmares.