How does Frankl describe a "delusion of reprieve"?

Frankl writes that "the condemned man, immediately before his execution, gets the illusion that he might be reprieved at the very last minute. We, too, clung to shreds of hope and believed to the last moment that it would not be so bad." In many things, as he enters Auschwitz, Frankl finds signs of hope, but he later learns that these signs he initially saw as hopeful did not really help his experience of life in camp.