Dark doubles are a recurring theme in Supernatural. What is more frightening, more eerie, than to think of there being another one of you out there, someone who looks like you, who maybe even shares your DNA, but is definitively not you? One of my favorite films of all time, The Double Life of Veronique takes this concept as its main topic.
Veronique grows up feeling like she is missing something, a part of herself. Sam and Dean Winchester are split off from parts of themselves. Splitting off means you actually survive. Sometimes they are confronted with their future selves, or with their dark-side selves. And in one episode, terribly, the brothers are basically cloned and then proceed to go on a killing spree across the country. This brings their split-off selves into terrifying Kafka-esque territory, where the bureaucracy amassing its powers against you is too powerful to fight.
How on earth can you explain that that killer seen on all the security cameras is not actually you, when it looks like you, has your fingerprints, your DNA? The only time it rises up to confront him is in his nightmares, there every time he closes his eyes, and then in the final confrontation with his steely double in the mirror.
There would be friends and fellow students, people who loved Sam, who would wonder where the hell he had gone. Dean, as we know already, or we certainly guess, has no friends. While Dean seems gregarious, and weirdly extroverted, he is also truly solitary.
One of the things I absolutely love in later episodes is how Dean, even with his weirdness, can fit in everywhere. Throw him into a situation where he is a PA on a Hollywood movie? Throw him in prison? Have him suddenly be a high school gym teacher? They are whatever you want them to be. He seemed to inspire intimacy, he worked with his hands, he was basically pan-sexual, grease under his fingertips, and a magnet for awesome-ness.
