The meaning of this sentence is: you only need to wait for the time to stab the wounded tiger, that is two tigers in one go.

Source: "Strategies of the Warring States - Guan Zhuangzi Stabbing a Tiger"

Original text:

There were two tigers fighting over a man, and Guan Zhuangzi was going to stab him. The two tigers were fighting over a man, and Guan Zhuangzi was about to stab him. Guan and Zhuangzi stopped him by saying, "The tiger is a hostile insect; the man is a sweet bait. Now the two tigers fighting for people and fighting, the small will die, the big save will be injured. Zi to be wounded tiger and stabbed, it is a move and both tigers. There is no labor in stabbing one tiger, but there is the name of stabbing two tigers."

Translation:

There were two tigers fighting over a man, and Guan Zhuangzi was about to stab them, but Guan and stopped him, saying, "The tiger is a greedy and brutal animal, and man is its most delicious food. Now the two tigers are fighting over a man, the weaker tiger will surely die, and the stronger one will surely be wounded. All you have to do is to wait for the right moment to assassinate the wounded tiger, and you will get two tigers in one go. Without paying the labor of stabbing one tiger, you have the fame of stabbing two tigers to death."

Expanded:

During the Warring States period, war broke out between Han and Wei for more than a year, and there was still no winner or loser. King Hui of Qin intended to send troops to intervene, just as the envoy of Chu, Chen Jing, arrived, King Hui of Qin knew that Chen Jing was very insightful, so he asked him for advice. Chen Jing then told this story to King Hui of Qin.

Chen Jing said to King Hui of Qin, "Now Han and Wei are in a long war, and in the end, the weaker state will surely perish and the stronger state will be greatly weakened. At this time, if you take advantage of the situation to defeat the weakened strong state, isn't it the same as destroying the two countries at once?" King Hui of Qin listened to Chen Jing's advice, and was indeed victorious. Based on this story, later people used the idiom of "two defeats and two wounds" to describe the loss of both sides in the struggle.