Perhaps our individuality in life is ultimately related to our fundamental interchangeability as subjects in a similar way. The difference between us, like the differences between observers, may be at the deepest level a function of separation in space and time. Like elementary particles, we are numerically distinct while identical in essence. We think of ourselves as separate because we identify with the distinct location in space of the body, and we think of ourselves as unique because we identify with the history of the body in time. At this level there appears to be great diversity of experience, circumstance, ability and character.
Some people suffer incredible hardship while others are blessed with comfort and ease.
To be a particular self, an ego, is to have a special relationship to that part of the world that is one's own body. Both concern one's own body in a different way than other bodies in the universe. This relationship is not epistemically special, but physically and affectively special. This is so because the same distinction that is supposed to split the subject off within the field of experience, as a private inner domain, occurs within the subject itself. To observe one's experience is a different stance than believing it.