“Hedonic treadmill” refers to the tendency to always go back to the same level of happiness despite positive life events. Personal happiness does seem to increase as family incomes rise, a phenomenon apparent in both the U.S. and Britain. But once we reach a modest level of income, more money doesn't bring greater satisfaction. This is when we find ourselves on what experts call the “hedonic treadmill”.

“快樂水車”指盡管經歷了本該令人快樂的事情，人們卻并沒有變得更快樂的現象。隨著家庭收入的增長，個體的幸福感會增強，這種現象在美國和英國很常見。但是一旦人們的收入達到了一定水平，收入的增加卻不能再帶來更多的快樂。這時，人們就陷入了“快樂水車”時期。

Social scientists explain this happiness plateau through the "aspiration adjustment hypothesis." As soon as we acquire a moderate amount of wealth, our expectations rise for a higher quality of life. When we don't reach these new levels, our spirits flag, leaving us disillusioned.

社會學家用“期望調適假說”來解釋這種高原現象。一旦我們獲得了一定的財富之后，對于生活品質的期望值便會增加。如果不能達到這些新的高度，我們就會一蹶不振，感到幻想破滅。

A second explanation comes from the idea of "relative position": We compare our wealth and place in the social hierarchy to those around us. No matter how high we climb, we almost always encounter someone who is richer or who has more things.

我們還可以從“相對位置”這一概念中找到解釋。我們往往會將自己的財富和社會地位與身邊的人進行比較。不管我們在成功的路上爬得有多高，我們幾乎總是可以碰到比自己更富有或擁有更多的人。

（中國日報網英語點津 實習生 陳思迪）