His mind would wander, and he would lose track of what he was doing.

他会心不在焉起来，忘了自己刚才正在干什么。

You become so deeply absorbed in an activity that you lose track of time.

你是那么专注于一项活动，以致忘了时间。

You lose track of time and there is nothing but the croissant in your life.

你忘记了时间，生活中除了牛角面包什么都没有。

Don't lose track of your goals.

不要迷失你的目标。

I quickly lose track of her.

我在人群中失去了她的踪迹。