One reason why birds and horses are happy is because they are not trying to impress other birds and horses.

Carnegie’s line contrasts animal contentment with human social anxiety. Birds and horses, in this framing, live without the self-conscious performance that drives much human unhappiness—status-seeking, comparison, and the pressure to curate an image for peers. The remark fits Carnegie’s broader self-help ethic: peace of mind and effective living come less from external approval than from focusing on genuine purpose, character, and practical action. By using familiar animals, the quote makes a moral point feel obvious and disarming: much of our distress is optional, created by the imagined audience in our heads. It implicitly recommends humility and authenticity as routes to happiness.