Carl Sagan, Pale Blue Dot: A Vision of the Human Future in Space

"The visions we offer our children shape the future. It _matters_ what those visions are. Often they become self-fulfilling prophecies. Dreams are maps."

"A blade of grass is a commonplace on Earth; it would be a miracle on Mars. Our descendants on Mars will know the value of a patch of green. And if a blade of grass is priceless, what is the value of a human being?"