Qian Che Zhi Jian (A Warning Taken From the Overturned Cart Ahead)
During the Western Han dynasty, there lived in Loyang a man named Jia Yi. Jia Yi was very knowledgeable , and even the emperor engaged him as a teacher. One day, he was teaching the emperor about the proper way to govern a country. He said, "During the Qin dynasty, there was an evil minister named Zhao Gao, who was the teacher of Hu Hai, the emperor's second son. He ofter taught Hu Hai how to destroy one's political opponents, and often talked of how to execute prisoners."
"After his father's death, Hu Hai became emperor. On the second day of his reign, he began to kill people, and would not listen to those who tried to give him advice. In reality, Hu Hai was not a bad person, but in the end, he was overthrown."
Jia Yi continued, "Knowing the mistake made by our elders, we should be careful not to make the same ones ourselves. It's the same way as if we are out driving and see that the poor road ahead of us has caused a cart to overturn. We should learn from this, and not take the same road."
Thus, "A Warning Taken From the Overturned Cart Ahead" means seeing the mistake that someone else has made, and not making the same mistake ourselves.