An individual may be alone in a physical sense for many years and yet he may be related to ideas, values, or at least social patterns that give him a feeling of communion and "belonging." On the other hand, he may live among people and yet be overcome with an utter feeling of isolation, the outcome of which, if it transcends a certain limit, is the state of insanity which schizophrenic disturbances present.
Erich Fromm, Escape from Freedom
philosophy, psychology