“How can something be possible, yet not practical?” “It is theoretically possible for me to visit each world of the Galaxy and greet each person on each world. However, it would take far longer to do this than I have years to live and, even if I was immortal, the rate at which new human beings are being born is greater than the rate at which I could interview the old and, even more to the point, old human beings would die in great numbers before I could ever get to them.”
