An opportunity like this comes once in a lifetime.

像这样的机会一生也许只会遇到一次。

《牛津词典》

On the positive side, we have all the extremes in pessimism that typically accompany a bear-market bottom — a once-in-a-lifetime buying opportunity.

从乐观的角度来看，市场上已经出现了所有伴随熊市底部出现的极端悲观情绪，因此现在是一个千载难逢的买入机会。

youdao

Carl: You can't pass up this job.This kind of opportunity comes only once in a lifetime.

卡尔：你不可错过这个工作。这种机会一辈子才有一次。

youdao

For the fans,it will be a once-in-a-lifetime opportunity to join the celebrations and see the world's greatest football players compete at home in Africa.

VOA: standard.2010.02.10

And then other people are really excited because it's a once-in-a-lifetime opportunity

而另外一些人真的很兴奋，因为这是一个一生只有一次的机会，

正准备奥运会 - SpeakingMax英语口语达人

The whole nation has to get behind the legacy values here because this is a once-in-a-lifetime opportunity.

BBC: Olympic Games: Lord Coe made legacy ambassador

It was a once-in-a-lifetime opportunity for the club and it's awesome that we came out on the right side of it.

BBC: Cockerill hails Leicester scrum

This is a once-in-a-lifetime opportunity for visitors to name a new species.

BBC: Forensic science uncovered