In fact the whole antithesis between self and the rest of the world, which is implied in the doctrine of self-denial, disappears as soon as we have any genuine interest in persons or things outside ourselves. Through such interests a man comes to feel himself part of the stream of life, not a hard separate entity like a billiard-ball, which can have no relation with other such entities except that of collision.

Bertrand Russell (1872–1970) English mathematician and philosopher

Conquest of Happiness, Part 2, ch. 17 “The Happy Man” (1930)
    (Source)