The individual is defined only by his relationship to the world and to other individuals; he exists only by transcending himself, and his freedom can be achieved only through the freedom of others. He justifies his existence by a movement which, like freedom, springs from his heart but which leads outside of himself.
Martin Heidegger, Simone de Beauvoir, Jean-Paul Sartre (2016). “The Philosophical Library Existentialism Collection: Essays in Metaphysics, The Ethics of Ambiguity, and The Philosophy of Existentialism”, p.133, Open Road Media