" What if there are not only two nostrils, two eyes, two lobes, and so forth, but two psyches as well, and they are separately equipped? They go through life like Siamese twins inside one person. Everything that happens to one, happens to the other. If one gets married, the other is along for the ride. Otherwise, they are different. They can be just a little different, like identical twins, or they can be vastly different, like good and evil.” She stopped for a nearer example. “Or optimism and pessimism. "

― Norman Mailer , Harlot's Ghost