The events that take place in Boyne's work happen because people do not take action to fully prevent them. This becomes the cautionary tale behind The Boy in the Striped Pajamas.
While Boyne's work deals with a vast topic, its focus is a very human one. The work does not look at the rise of Nazism and the Holocaust from social, political, or economic dynamics. Rather, its presentation focuses on the actions of human beings. For example, Bruno's father is excited about the career advancement opportunities at being placed in charge at "Out- With." When he rejects the pleas from Bruno's grandmother to stop participating in brutality, it is clear that he is making a conscious choice, one he comes to regret upon finding out the truth of what happened to Bruno. This same element applies to Bruno's mother. She knows what is happening in Auschwitz and wants to protect her children. However, when she leaves with Gretel back to Berlin, it is clear that her action was taken too late. Her opposition in the form of departure is what she should have done when Bruno was alive. Once again, a person's action is a critical entity when explaining the presence of human suffering. Bruno represents the ability to take action on the opposite side of the equation. In standing up for Shmuel, he does what he believes is right. Nazism and the Holocaust might have been averted if more people acted like Bruno did. Boyne is suggesting that human beings can take action that either stands up for the rights of others or increases the suffering of other people.
Such a message is the reason why the novel operates as a cautionary tale. Throughout the world, there are situations where people have the power to stop human suffering or perpetuate it. While we might suggest that there are elements outside of our control, Boyne seems to be arguing that on the smallest of levels, we can take action to either stop injustice or increase its presence. Such a revelation is what reminds the reader that events such as what was shown in the book could happen again if human beings are not vigilant and mindful of the role they play.