Charley, in "Of Missing Persons" by Jack Finney is a young man who lives life simply by putting one foot in front of the other, day after dreary day.
Charley's life is one of drudgery and unhappiness. He has no friends and spends too much time alone. He lives in the cold city, working in a job with no future; he feels he is "selling" his days just to survive.
However, Charley has been told by a man at a bar that there is another place he can go. And that if he follows the directions given to him--by someone who has been there--he can find a second chance, and realize his dreams of a new life.
He is filled with self-doubt, and he doubts the possibility that there could be anything out there better that could be his. What he has offers him no hope and certainly no comfort or satisfaction.
So Charley goes to the travel agency, and he sees the promise of a new life laid out before him. He is "tested" by the man across the counter who sees the hunger for a better life in Charley's face, in his eyes. Through the process, however, we see his self-doubt: Charley is unsure that he will be found acceptable, that he will ask the right questions or behave in a way that would win the other man's approval, but--in fact--he does. And so the arrangements are made.
Charley follows all the directions the man gives him, after measuring carefully whether he is willing to give up what little he has in order to achieve "everything" he hopes for. He decides that he cannot go back to the life he knew, and he plans to move to a new world.
But Charley is still too filled with self-doubt; he has been beaten down too often by an uncharitable world. He knows what he wants, but he cannot believe that it can be his, just for the asking. And when the moment is upon him to truly decide, he loses faith, feels he has been played as a fool, and forever misses the opportunity before him: in doing so, he now is left with what little he had before, and a sense now of certainty of what he lost because he could not find it in himself to simply believe.
The man at the bar at the beginning of the story had been there, and tried to help Charley learn by his own mistakes. The man's directions at the start of the story, come back o haunt Charley:
...if you're the type, if you can believe—then make up your mind and stick to it! Because you won't ever get a second chance. I know...
This, then, is an allegorical story about life: opportunity comes to us, and if we believe, we can achieve what others cannot, but there are no second chances when opportunity knocks and we fail to answer.
Charley does not believe enough in himself and that which he must take on faith to stick to it, and he loses his chance to change his world.