春秋时代，齐国向鲁国发起攻击。
鲁庄公和他的顾问曹刿一起率军迎战。
两军在长勺这个地方摆开阵势，准备决一死战。
首先，齐军擂响了第一次鼓，鲁庄公听到后也打算下令击鼓进攻。
但是，曹刿阻止了他：“不行，还不到时候。”
于是，他们继续等待。
齐军接着又擂响了第二次、第三次鼓，但曹刿仍然没有发出进攻的命令。
直到齐军第三次擂鼓结束后，曹刿才说：“现在可以击鼓进攻了！”
他的话音刚落，鲁军的战鼓就“咚、咚、咚”地响了起来。
这声鼓响如同闪电一般激起了鲁军士兵们的士气。
他们像猛虎下山一样冲向敌军，结果齐军被打得大败而逃。
然而，当鲁庄公想乘胜追击时，曹刿再次阻止了他：“现在还不是时候。”
说完，他就下车仔细观察敌军留下的车迹和散落的旌旗，确定敌人是真的溃败了，才告诉鲁庄公：“现在可以追击了。”
果然，在这次追击中，鲁军把齐军打得落花流水，取得了胜利。
事后，鲁庄公问曹刿为什么要等到齐军第三次擂鼓后才下令进攻。
曹刿回答说：“打仗全靠一股勇气。第一声鼓响时，士兵们的勇气最旺盛；第二声鼓响时，勇气就会有所衰退；到了第三声鼓响时，大家的勇气就已经消失殆尽了。这时，如果我们再击鼓进攻，就可以利用我们的勇气优势打败敌人。”
他还解释了自己下车观察的原因：“我担心齐军会有埋伏，故意引诱我们上当。当我看到他们的军队车迹混乱，旗帜歪斜倒地时，我才断定他们是真的惨败，才敢放心追击。”
从此以后，“一鼓作气”这个成语就被用来比喻做事要鼓足勇气，勇往直前，才能一举成功。
During the Spring and Autumn period, the state of Qi launched an attack on the state of Lu.
Lu Zhuanggong and his advisor Cao Gui led their army to meet the enemy.
The two armies faced each other at a place called Changshuo, ready for a decisive battle.
First, the Qi army sounded the first drumbeat. When Lu Zhuanggong heard it, he also wanted to order the drums to signal an attack.
But Cao Gui stopped him: "No, it's not time yet."
So they continued to wait.
The Qi army then sounded the second and third drumbeats, but Cao Gui still did not give the command to attack.
It was not until after the third drumbeat of the Qi army that Cao Gui said, "Now we can sound the drums and attack!"
As soon as he finished speaking, the war drums of the Lu army thundered out with a loud "dong dong dong."
This drumming was like lightning, igniting the morale of the Lu soldiers.
They charged towards the enemy like tigers descending from the mountains, and as a result, the Qi army was defeated and fled in disarray.
However, when Lu Zhuanggong wanted to pursue the retreating enemy, Cao Gui stopped him again: "It's not time yet."
After saying this, he got off his chariot and carefully observed the tracks left by the enemy's chariots and the scattered banners, making sure that the enemy had truly retreated before telling Lu Zhuanggong, "Now we can pursue them."
Sure enough, in this pursuit, the Lu army thoroughly defeated the Qi army and emerged victorious.
Afterward, Lu Zhuanggong asked Cao Gui why he waited until the third drumbeat of the Qi army to order an attack.
Cao Gui replied: "Victory in battle depends entirely on courage. At the first drumbeat, the soldiers' courage is at its peak; at the second drumbeat, their courage begins to wane; and by the third drumbeat, everyone's courage has been exhausted. It is at this time that if we sound our drums and attack, we can take advantage of our superiority in courage to defeat the enemy."
He also explained the reason for getting off his chariot to observe: "I was afraid that the Qi army might have an ambush, deliberately luring us into a trap. When I saw their chaotic chariot tracks and flags lying askew on the ground, I was convinced that they had suffered a true rout, and only then did I dare to pursue them with confidence."
From then on, the idiom 'With One Heart' has been used to比喻做事要鼓足勇气,勇往直前，才能一举成功.
