He sent me on a fool's errand.

他派我去干白费力的事。

《牛津词典》

A fool's errand, you say.

你会说，这还真是愚蠢的行为。

youdao

Even in quiet times, predicting the paths of exchange rates is a fool's errand.

即便在市场平稳的时候，预测汇率走势也是一件费力不讨好的事。

youdao

Until you're a proficient reader of a language, writing in our language is a fool's errand.

你只有成为一个熟练的读者，才有可能成为一个好的作者。

英语阅读：技巧 - SpeakingMax英语口语达人

Given that most stock options in new start-up companies are never worth anything, this would seem a fool's errand.

WSJ: Washington Is Killing Silicon Valley

But bringing them down close to zero, in government or in any other sphere, will remain a fool's errand.

ECONOMIST: The price of prudence

What they told members of the Senate Foreign Relations Committee ranged from tentative support for the plan to calling it a fool's errand.

NPR: Retired Army Generals Criticize Bush's Iraq Plan