一yī鼓gǔ作zuò气qì

Literal: at the first drumbeat the spirit rises
Figurative: To seize the initial burst of energy and finish something in one sustained effort, without pauses that let momentum cool; to get it done in one go while morale is high.

Where does 一鼓作气 come from?

In 684 BC the state of Qi attacked the state of Lu. The strategist Cao Gui accompanied Duke Zhuang of Lu to the battle of Changshao. When Qi's war drums sounded the charge for the first time, Cao Gui held Lu back; he did the same at the second beat. Only when Qi drummed a third time did he order the attack, and Lu won. He later explained that battle rests on morale: the first drumbeat fires the spirit up, the second lets it flag, and by the third it is spent. Lu struck with its courage intact just as the enemy's had drained away.

Source (出处): 《左传·庄公十年》

How is 一鼓作气 used? Two examples

趁chèn着zhe大dà家jiā都dōu有yǒu精jīng神shén，我wǒ们men一yī鼓gǔ作zuò气qì把bǎ这zhè个ge项xiàng目mù做zuò完wán吧ba。
While everyone's still energized, let's finish this project in one go.
复fù习xí就jiù要yào一yī鼓gǔ作zuò气qì，中zhōng间jiān一yī停tíng下xià来lái就jiù很hěn难nán再zài开kāi始shǐ了le。
You should study in one sustained push; once you stop halfway, it's very hard to get going again.

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