It is used when someone tells something that was supposed to be secret.

VOA: special.2009.01.25

The New Criticism, incontestably and without rival, created an atmosphere in which it was okay to notice that things were a little more difficult than they'd been supposed to be.

新批评派，无可厚非，创造了一种很好的风气，大家似乎都能欣然接受,那些看起来还比较复杂的东西。

耶鲁公开课 - 文学理论导论课程节选

You found, I don't remember his stagefright Well, I think there was one moment in his scene like he's standing in front of a crowd, it is supposed to be on a ship, I think.

我不记得他怯场,我想在他镜头中有一次,好想他站在一群人当中，我觉得应该是在一艘船上。

麻省理工公开课 - 电影哲学课程节选