Our sense of the preciousness of other people is connected with their power to affect us in ways we cannot fathom and in ways against which we can protect ourselves only at the cost of becoming shallow. There is nothing reasonable in the fact that another person's absence can make our lives seem empty. The power of human beings to affect one another in ways beyond reason and beyond merit has offended rationalists and moralists since the dawn of thought, but it is partly what yields to us that sense of human individuality which we express when we say that human beings are unique and irreplaceable. Such attachments, and the joy and the grief which they may cause, condition our sense of preciousness of human beings. Love is the most important of them.