The essence of training is to allow error without consequence. Three-dimensional warfare would need to be practiced in an enclosed space, so mistakes wouldn't send trainees flying off to Jupiter. It would need to offer a way to practice shooting without risk of injury; and yet trainees who were "hit" would need to be disabled, at least temporarily. The environment would need to be changeable, to simulate the different conditions of warfare--near a ship, in the midst of debris, near tiny asteroids. And it would need to have some of the confusion of real battle, so that the play-combat didn't evolve into something as rigid and formal as the meaningless marching and maneuvers that still waste an astonishing amount of a trainee's precious hours in basic training in our modem military.

The result of my speculations that morning was the Battle Room, exactly as you will see it (or have already seen it) in this book. It was a good idea, and something like it will certainly be used for training if ever there is a manned military in space. (Something very much like it has already been used in various amusement halls throughout America.)

But, having thought of the Battle Room, I hadn't the faintest idea of how to go about turning the idea into a story. It occurred to me then for the first time that the idea of the story is nothing compared to the importance of knowing how to find a character and a story to tell around that idea. Asimov, having had the idea of paralleling The Decline and Fall, still had no story; his genius--and the soul of the story--came when he personalized his history, making the psychohistorian Hari Seldon the god-figure, the planmaker, the apocalyptic prophet of the story. I had no such character, and no idea of how to make one.