Mortals do not want to face their own mortality, and any acknowledgement of wraiths means that they must also acknowledge that they too will one day die. "The Fog" is the name wraiths ascribe to mortals’ instinctive denial of their existence. Mortals affected by the Fog react to wraiths in a variety of bizarre ways, but inevitably block the encounter from memory similar to Delirium that the Fera inflict upon their victims.
Those who do not comprehend the terror of death (animals, children, the insane, etc.) are not affected by the Fog.