The Third Man is a phenomenon reported by some wilderness survivors---namely those in cold climates (mountain climbers etc). They'll report talking to, having whole conversations with and interacting with a nonexistent entity called the 'Third Man'. So named because of a team of two climbers who both felt as though there was a third person with them, despite knowing they were the only ones there. Some say it's just a feeling of not being alone and relate it to a religious experience. Some say they're literally not alone, and that there's something which likes to hang around humans who are extremely isolated from others (we're talking miles and miles away from the nearest human, in extreme circumstances). My take is that it's hypothermia related, or maybe has something to do with nerves deadening. You 'feel' like someone else is there because you're becoming less aware of your own body. Hear breathing that you no longer identify as yours. Steps in the snow you no longer identify as yours. But that's just my guess and, honestly, it isn't supported by science. Many of those reporting the sensation are perfectly healthy. Did not experience hypothermia or starvation on their trip. Psychologically 'normal'. Just absolutely certain there was an extra person, or an extra something, with them. This extra person never seems to do anything, just follow along. 'It wasn't me, it was the Third Man' suggests, creepily, that if the Third Man were to start DOING things (like, I don't know, killing people) it'd probably be a real bad day. Or someone thinking the Third Man was doing it when they were actually the one... you know. That sort of psychological rabbit hole.