Personalities are a fluid property that begins to develop from the moment of birth. Comprised of experiences that get stored as memories; these key moments establish expectations and reactions to stimulus. The fragility of a child's psyche leaves it vulnerable to sociopathic behavior if dramatic events occur. On December 22nd, Kevin McCallister experienced the first moment in a string of events that would change his life forever.
I had this idea from last year based on a fan theory stating that Kevin McCallister grows up to be Jigsaw from the SAW series!