Self

Because no two objects can occupy the same place at the same time, no two people can look at the universe from the exact same viewpoint. Two people might trade locations to get a view from the other person's point in space, but they would each have been looking from that place at different points in time.

This is what makes people truly unique, and not our superficial differences. The various physical and mental characteristics of each person add to that uniqueness, but individuality is guaranteed because each person, even an identical twin, is the center of his own perceptual universe.