一 + 动词 + 就是 + 时量
once (someone) starts, it goes on for (a long time)
Structure
（宾语，） 一 动词 就是 时间／数量
What it means
'Once (someone) starts, it goes on for (a long time)': stresses that the time, or the amount, is large.
How it is built
(Object，) 一 + verb + 就是 + time or amount: 他喜欢钓鱼，一钓就是一整天 (he loves fishing; once he starts, he is at it all day). Also 一买就是十斤.
When to use it
Spoken and narrative, often about habits. Typical lengths: 一上午, 一整天, 半天, 好几年. Plain 一…就… means 'as soon as': 他一到就开始了.
Watch out
The verb usually appears bare, its object named earlier: ✓喜欢钓鱼，一钓就是一整天。 It stresses a large amount, so a small one sounds odd: ✗一睡就是五分钟。
Examples
老人们打太极拳，一打就是一个多小时。
Once the old people start their tai chi, they keep going for over an hour.
他喜欢钓鱼，一钓就是一整天。
He loves fishing; once he starts, he is at it all day.
外婆说起过去的事，一说就是半天。
Once Grandma starts on the old days, she goes on for ages.
Learn this in Lesson 13 · HSK 5: 公园里的中国 (A morning in a Chinese park)
A dialogue, a reading, word cards with audio and a drill that uses it, in Learn Chinese with Bao. The first lessons of every level are free.
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