Symbolism, Imagery, Allegory
Finders, keepers—that's what a flag on a piece of land means, right? Especially if it's an American flag—the only flag—on the moon. So right off, the flag on the moon should tip you off as a symbol of American power and American ownership.
And yeah—it's an amazing historical event. "A flag on the moon! Isn't that splendid?" Mrs. Croft keeps repeating throughout the story.
But how does that "splendid" event compare to the narrator's personal achievements? Which one is greater? As the narrator points out:
While the astronauts, heroes forever, spent mere hours on the moon, I have remained in this new world for nearly thirty years. I know that my achievement is quite ordinary. I am not the only man to seek his fortune far from home, and certainly I am not the first. Still, there are times I am bewildered by each mile I have traveled, each meal I have eaten, each person I have known, each room in which I have slept. As ordinary as it all appears, there are times when it is beyond my imagination. (TFC 151)
"One step for mankind"? Not to take away from that metonym—"one step" for (hu)man progress—but the narrator refocuses us on what (hu)man progress can (and maybe should) really mean: how an ordinary person lives.
In other words, what if we were to think about success and achievement apart from some dramatic accomplishment or conquering distant real estate? Wouldn't that be pretty amazing, too?