The philosopher Arthur Schopenhauer formulated a metaphor called the porcupine dilemma, which explains a certain optimal distance between people. People feel alone at too large a spacing and uneasy at too close a proximity. Schopenhauer explained the ideal spacing using the following parable: "A number of porcupines huddled together for warmth on a cold day in winter; but as they began to prick one another with their quills, they were obliged to disperse. However, the cold drove them together again, when just the same thing happened. At last, after many turns of huddling and dispersing, they discovered that they would be best off by remaining at a little distance from one another. In the same way, the need of society drives the human porcupines together, only to be mutually repelled by the many prickly and disagreeable qualities of their nature."