Why won't the other Jews believe Hannah when she tells them the Nazis is going to kill them?

Hannah finds that no one will believe her about the danger they are in. Her stories about the gas ovens are quickly dismissed as being derived from fairy tales like Hansel and Gretel. This highlights the incomprehensible evil that the Holocaust embodied. It is not difficult for us to understand how the others Hannah tries to warn would not believe such stories, as they seem beyond possibility. The sheer size of such an abhorrent undertaking only added to its tragedy.