So Bob is also Charlie, maybe even with a little Albert hiding in there somewhere. There are many possible reasons for the existence of these split personalities, but this co-habitation is rarely peaceful or long lasting. It usually results in a Battle in the Center of the Mind to try and find out which personality will take over. Sometimes though, the winner might not reduce the loser to a tiny, powerless voice or destroy it completely, and instead offers to become one again. With a little Epiphany Therapy, Applied Phlebotinum or even actual psychotherapy, they merge into a single, whole person that is greater than the sum of its minds.