It is either because he has a wife or because the fact that he has a wife means that he is not lonely that the young waiter expresses some optimism in his outlook.
The old man is at a different stage of his life from both the young and middle-aged waiters. What then is the theme of this story?
He recognises himself in the old man and he knows his own life is lonely. A young waiter is angry; he wishes that the old man would leave so that he and an older waiter could close the cafe and go home. Emotional darkness is the first component that must be unfolded when analyzing the theme of the story.
The old man has his dignity.
What may cause his lack of sleep is the fact that he is aware that his life means nothing, a dark reality for any person.