I’m reading The Third Man Factor a book about the phenomenon named after a poem based on Shackleton’s story of survival in 1916. Shackleton felt the presence of an invisible person helping his group survive. This book tells the stories of survivors who felt a presence that helped them struggle through life and death situations. Author’s website here. NPR story here.
“One of the most famous instances of the phenomenon took place during Ernest Shackleton's Antarctic expedition in 1916. The team's boat was trapped in ice and they were forced to make a grueling journey across mountain ranges and glaciers to a whaling station in Stromness Bay. Shackleton later wrote: ‘I know that during that long and racking march of thirty-six hours over the unnamed mountains and glaciers, it seemed to me often that we were four, not three’.”