On a cold winter’s day, porcupines huddled together to keep warm. But, as they huddled together, they soon felt the burning sting of their quills and they had to separate. When they grew cold, their instinct was to move even closer together… But again, they felt the burning sting of their quills. They repeated this manoeuvre several times until they finally found the right distance. Fable told by German philosopher Schopenhauer (1788–1860).