The airmen don't fly until they're needed. That means waiting, sometimes for hours or even days.

VOA: standard.2010.04.27

Any thoughts? Don't you hate professors who stand here waiting for you to answer, even when they have candy?

你们难道不讨厌站在那儿等你回答问题,的教授么？虽然他有糖果做奖品哦，用少于线性时间完成可能么？

麻省理工公开课 - 计算机科学及编程导论课程节选

And again, you don't teach an animal to play Ping-Pong by waiting for it to play Ping-Pong and then rewarding it.

同样，你并不能通过等待动物打乒乓球,然后给其奖励,来使动物学会打乒乓球。

耶鲁公开课 - 心理学导论课程节选