How did Hans survive when Erik Vandenburg didn’t

During WW1, Hans befriends a German Jew named Erik Vandenburg, who teaches Hans to play the accordion. The day the platoom is to go into battle, the Sergeant asks which one of them has good handwriting. None volunteered. The Sergeant says that whichever man does will not be going into battle, yet no man wants to seem like a coward. Erik nominates Hans, who is sent to write letters for the captain. The rest of the men are all killed.