Story: During the Warring States period, the powerful state of Qi dispatches troops to attack the state of Lu. King of Lu leads his troops personally, ready to battle it out.
"The Qi army is ready to attack us. I order you all to get ready to fight back!"
"Your Majesty, now it is not opportune to fight back. I suggest we wait a moment."
Seeing no response from the Lu army, the Qi army beat their battle drums again.
"Now, should we send out our troops?"
"We have to wait another moment."
The Qi army beat their drums for the third time. The Lu King throws a quick glance at Cao Gui. But Cao Gui keeps silent. The Qi army's third drumming has stopped.
"Your Majesty, now we can hit back."
"Good. Beat our drums and hit back!"
The Lu army goes all out and beats the Qi army. After the war is over, the Lu King asks Cao Gui: "Why did we have to wait until the Qi army's third drumming before we launched the attack?"
"Fighting relies on the soldiers' courage. After the first drumming, the enemy soldiers' morale was the highest. After the second drumming, their morale became weaker. And after the third drumming, their morale was completely gone. When our army sounded our drums, our buoyant troops would certainly beat the slack and tired enemy."
do sth. At one go; press on to the finish without letup; get sth. Done in one vigorous effort
He got up from the bed and finished the letter at one go.