before you know it 不知不觉;很快;不知不觉中

【例句】
Before you know it, you've squandered3 a couple of perfectly4 good hours of prime workday.
不知不觉，你已经把好几个小时的黄金工作时间耗费在那里了。

Before you know it, you're smoking three packs a day.
不知不觉，你又会一天抽三包了。