During the Eastern Jin Dynasty, continuous wars occurred among the powerful aristocratic families. Among them, General Yu Liang held the greatest influence. He wielded central power and was highly regarded by Emperor Cheng. The Emperor always sought his advice on important court matters.

However, General Su Jun, who was stationed in Liyang, was greatly displeased, thinking, "I have achieved numerous military successes on the battlefield, so why does Yu Liang rise so swiftly?" Consequently, he ordered his subordinates to launch an attack on Yu Liang.

News of this reached Governor Wen Qiao, who was stationed near Lei Pond. Upon hearing that Yu Liang was under siege, he immediately prepared to dispatch troops for rescue. Unexpectedly, Yu Liang sent him a letter, explicitly instructing him, "Do not cross Lei Pond one step!"

Yu Liang explained that if Lei Pond were to fall, Liyang would also be lost. The original meaning of this idiom was to instruct Wen Qiao to firmly hold his defensive position and not to advance towards the capital.

Today, it is used to describe someone who dares not exceed certain boundaries or limits in their actions.