Albert Camus's story "The Guest" illustrates how difficult it is to sometimes make the right decisions. Daru was faced with the choice of whether or not he should follow orders and hand over the Arab to police headquarters. He does not want to make this decision and is relieved when he thinks the Arab is going to run away in the middle of the night. However, the Arab returns. In the end, Daru leaves the choice up to the Arab as to whether he should pay for his crime, or go free. Surprisingly, the Arab chooses to go to prison.
The dilemmas presented in this story are not simple ones. There is no black and white or clear resolution to the decision. Daru simply handing over the Arab to the authorities would be "contrary to honor" (p 255). Yet, the murder of the Arab's cousin was so revolting that Daru believed he should be punished. Daru knew that he was in no position to decide the fate of this stranger. Only the Arab could make the decision as to whether he would pay for his crime.
It is clear from reading this story that Albert Camus is an existentialist. He believes that every individual should have the freedom of choice and be responsible for one's own actions. I think the character of Daru is closely modeled after the author himself. By leaving the Arab to decide his fate, Daru is practicing existentialism.
It is unclear as to why the Arab does decide to turn himself in. He could have begun to feel guilty for his crime and decided that he deserved punishment. He could have realized that if he did not turn himself in Daru would have gotten into trouble. Or, maybe the uncertainty of what would happen if he took the trail to the nomads was too unsettling for him. However, I think if the author had let us know the Arab's reasoning behind this decision the theme of the story wouldn't have been as strong. The point was that he was left to make his decision on his own.