to be caught off guard by something意外遭遇
英文釋義
To be unprepared for something.
例句
Since the day had started without a cloud in the sky, we were caught off guard by the afternoon rainstorm that ruined our picnic in the park.
今天一早天空中還沒一絲云彩,下午卻下起了暴雨,破壞了我們在公園的野餐。