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

Carnegie contrasts human social anxiety with animals’ apparent ease to highlight how much unhappiness is self-inflicted through status-seeking. Birds and horses, he suggests, live without the constant comparative gaze—no performance for peers, no reputational scorekeeping—so they avoid a major source of worry and resentment. The remark fits Carnegie’s broader counsel that peace of mind and effective relationships come from reducing ego-driven display, focusing on sincere interest in others, and measuring life by inner standards rather than external approval. It is less a claim about animal psychology than a pointed metaphor about the costs of vanity and social competition.