Not hold one's breath 一是指没有在等待什么事发生；二是指不要寄太大希望.看下面的解释和例句：
An expression used to mean one is not awaiting something
例句：I'm hoping to hear if I got the job,but I'm not holding my breath.
It often is put as an imperative,don't hold your breath,meaning “don't expect it,it's not likely.”
例句：
They may get married this summer,but don't hold your breath.
This expression in effect implies it is unwise to stop breathing until a particular event occurs,since it may never come to pass.