All thinking, strictly speaking, is done in solitude and is a dialogue between me and myself; but this dialogue of the two-in-one does not lose contact with the world of my fellow-men because they are represented in the self with whom I lead the dialogue of thought. The problem of solitude is that this two-in-one needs the others in order to become one again: one unchangeable individual whose identity can never be mistaken for that of any other. For the confirmation of my identity I depend entirely upon other people; and it is the great saving grace of companionship for solitary men that it makes them “whole” again.

--- Hannah Arendt, "Ideology and Terror"