Third Man Syndrome

The Third Man Syndrome (also known as Third Man Factor) refers to the reported situations where an unseen presence such as a spirit provides comfort, solace or support during traumatic experiences.

[Wild South Georgia]

In his book 'South!: The Endurance Expedition', Sir Ernest Shackleton (1874–1922), described his belief that an incorporeal being joined him and two others during the final leg of their journey. Shackleton wrote, "When I look back at those days I have no doubt that Providence guided us, not only across those snowfields, but across the strom-white sea that seperated Elephant Island from our landing-pace on South-Georgia. I know that during that long and racking march of thirty-six hours over the unnamed mountains and glaciers of South Georgia, it seemed to me often that we were four, not three.".

[Shackleton's Endurance caught in the ice]

In 1933, British explorer Frank Smyth almost became the first person to reach the summit of Mount Everest. Unbeknownst to him, the rest of his team had fallen back, unable to make it through the sweeping wind, snow, ice and low oxygen. Smyth continued, but never made it to the top — he missed it by 1,000 feet. Later, writing in his diary, Smyth recounted how at one point on the ascent, he reached into his pocket, pulled out a slab of Kendal mint cake, broke it in half and turned around to give the other half to a companion. But there was no one there: "All the time that I was climbing alone, I had a strong feeling that I was accompanied by a second person. The feeling was so strong that it completely eliminated all loneliness I might otherwise have felt."
One study of cases involving adventurers reported that the largest group involved climbers, with solo sailors and shipwreck survivors being the second most common group, followed by polar explorers[1].

The syndrome was first clinically documented in the 1940s, psychologists have postulated various triggers and explanations ranging from sensory deprivation, extreme fatigue and boredom, to an evolutionary adaptation. If one person can summon up a benevolent presence while others are incapable of such a thing, then the psychological comfort may give a boost in the survival stakes. It is considered to be a coping mechanism or an example of bicameralism[2].

[1] Suedfeld, Geiger: The sensed presence as a coping resource in extreme environments in Miracles God, Science, and Psychology in the Paranormal (Vol.3) - 2008 
[2] McGregor: An adventurer’s guardian angel: the third man in Australian Geographic – 2012. See here.