What difficult lesson is Josef learning?

I think the main lesson is pretty depressing. No matter how hard some people try in getting to a safe country, many don't make it or die trying. Gratz uses Josef’s character to show how not all refugee children survive. Gratz shows that, despite doing everything they can to survive, sometimes the war is so terrible that the children cannot survive, and they are not to blame. Through taking Josef from Germany across an ocean, to multiple countries, Gratz shows how earnestly Josef and his family fought for survival. They did everything possible to find safety, even leaving behind Aaron, Josef’s father. However, Gratz shows that war can be so severe, and give no leeway to children, no matter how hard they try to escape.