Bolt 是閃電，blue 在這兒是指藍色的天空。 Like a bolt out of the blue 的意思就是晴天霹靂，也就是出乎意外、沒料想到。有時，你花幾個小時也解不開一道數學題。可是，當你不再去想它的時候，你腦子里突然出現了答案。人們還經常用 like a bolt out of the blue 來形容車禍。來看下面這個例子：

A driver may testify that he was going the normal speed limit when a truck appeared in front of him out of the blue and he did not have time to stop. 一個開車的人可能會在作證時說，正當他以正常的速度行駛的時候，一輛卡車突然出現在他面前，他來不及剎車。

我們再看看下面這個學生講的話:

The announcement that the president of our university was quitting to go to another school hit us like a bolt out of the blue. He’s always said he liked it here so much he would stay until he retired. 我們大學校長宣布他決定辭職到另外一個學校去工作。我們都感到很突然，因為他老是說他很喜歡這個學校，要一直在這兒工作到退休。