Those afflicted with depression (a mental disorder) see a world drained of all hope, happiness, and vigor. Even though they consciously know that it’s not so, since they can see everyone else being perfectly content, their subconscious can’t help but feel depressed. And so their immediate vicinity is steeped in the same dreariness and sadness, and affects the experiences others have of their surroundings. Likewise, people who aren’t depressed bring an aura of contentment with them - it’s not an aura that would be noticed by other, ordinarily content people, but it’s noticeable by whose who are depressed, which means depressed people can locate regular people even beyond line of sight, and vice versa. Depressed people would prefer the company of regular, content people as it lessens their gloomy aura, but everyone else (including other depressed people) wants to get away from them because they don’t want to be caught up in their web of depression, and this frequently results in them being ostracized and kicked out from settlements, forcing them to live their entire lives in the wilderness where there are few people to be bothered by them - or in prisons and slave pens, where both the depressed and the masters would be perfectly happy with them being, much to the anguish of the prisoners.