The existence of pleasure is the first mystery. The existence of pain has prompted far more philosophical speculation. Pleasure and pain need to be considered together; they are inseparable. Yet the space filled by each is perhaps different. Pleasure, defined as a sense of gratification, is essential for nature's workings. Otherwise there would be no impulse to satisfy the needs which ensure the body's and the species' survival. And survival—for reasons we do not know—is inwritten, inscribed as nature's only goal. Gratification, or its anticipation, acts as a goad. Pain or the fear of pain acts as a warning. Both are essential. The difference between them, considered as opposites, is that pleasure has a constant tendency to exceed its functional purpose, to not know its place.