" Early on December 25, Houston time, Lovell missed a step. He meant to enter Program 23 and then select Star 01. Instead, he entered Program 01 into his computer. An alarm rang out. Suddenly, Apollo 8’s guidance system reset itself, losing all memory of how the ship was oriented in space. As a result of Lovell’s mistake, the guidance system now believed Apollo 8 to be back on the launchpad at Cape Kennedy. "

― Robert Kurson , Rocket Men: The Daring Odyssey of Apollo 8 and the Astronauts Who Made Man's First Journey to the Moon