An optimist is a person who starts a new diet on Thanksgiving Day.

Kupcinet’s quip defines “optimism” through comic contradiction: beginning a diet on Thanksgiving—an American holiday centered on abundance and indulgence—seems almost willfully unrealistic. The joke hinges on the gap between intention and circumstance, poking fun at the human tendency to make self-improvement vows at the least practical moments. It also gently satirizes the cultural cycle of overeating followed by guilt and dieting, suggesting that optimism can shade into self-deception. At the same time, the line can be read more charitably: optimism is the stubborn belief that change is possible even when temptation is strongest.