Using someone else's knife to kill a person.
Interpretation:
The enemy is dangerous and in plain sight,
His intentions are obvious.
A friend can show deceit
And show your hidden strength.
To defeat the enemy,
You don't have to fight yourself.
We need to use the strength of a friend,
Solve your problems with someone else's knife.
When faced with the action of a third party, use its power to defeat your opponent.
Historical example:
One day, Cao Cao, a famous military leader, scientist and founder of the Wei Dynasty, wanted to meet the talented Ni Heng. Ni Heng was an expert in poetry, music and drumming, as well as a skilled calligrapher. He had a strong and proud character. However, the obstinate poet did not pay attention to Cao Cao, which greatly upset the military leader.
In response, Cao Cao appointed Ni Heng as a drummer in his army. Some time later, Cao Cao held a celebration on the island and intended to expose Ni Heng to ridicule in front of the guests. But Ni Heng, on the contrary, managed to ironically ridicule Cao Cao in a poem about the parrots given to him by his guests. As a result, this island began to be called Popugaev.
Founder Wei could not bear such insult. After this, Cao Cao came up with a cunning plan to take revenge on the arrogant poet, and said to his close associate:
“Ni Heng humiliated me, but he is very famous and respected.” If I kill him, I'll be accused of being petty. However, the warlord Liu Biao is known for his short temper and anger. I will send Ni Heng to serve him. Liu Biao will not stand it and will soon end his life.
And Cao Cao ensured that Ni Heng was transferred to Liu Biao's service. There he did not have to serve for long and sing his songs. As expected, one of Liu Biao's officers soon killed Ni Heng.