The estrangement of man from himself.
Non-acceptance of who we are and who we show the world. When man senses one meaning in experience, but the conscious self clings rigidly to please or seek approval from another, we are never really known. No one really sees or knows who we are, we are lonely in our being.
We feel the loneliness of not being in real touch with any other human being.
Modern man deserts his own experiencing to take on the way of being that will bring love. There is no security in any single facade.
Thus modern man experiences his loneliness, cut-off-ness, his isolation both from his own deeper self being hidden in fear of rejection. In seeking approval and love from others from a false self, one never can feel deep authentic approval and love.
We can show up authentically to others, showing our human side and when we give approval, love and compassion to ourselves, loneliness disappears.