STORY IDEA:

Everyone meets this one person.  Everyone then lives their lives without that person, making decisions furthering their future, and all decisions made were based on that one person's impact.

 So everything everyone does were influenced by that one person, however, upon making those conscious decisions, they do not think about that one person at all.

That person isn't remembered.  Everything was a subconscious decision triggered by memories of that person, but the person, he himself, isn't remembered.  And he lives his life, being alone, and suffering by his own mind, in internal solitary confinement.

Everyone else lives happily with their successful decision making, though their old friend isn't even acknowledged, or remembered.