During the Warring States Period, when Wei attacked Zhao, Zhao urgently sought help from Qi. King Wei of Qi planned to appoint Sun Bin as commander. Sun Bin declined, saying, "I am a man who has suffered punishment (referring to the cruel mutilation of his kneecaps by Pang Juan) and cannot bear such a heavy responsibility." The king then appointed Tian Ji as general, with Sun Bin serving as his military advisor, riding in a covered chariot to devise strategies.
Tian Ji was about to march his troops to Zhao's aid when Sun Bin advised, "Untangling a tangled knot requires more than brute force. A mediator doesn't join the fight but instead avoids the strong points and strikes where the enemy is weak, guiding events to resolve themselves. Right now, Wei and Zhao are locked in battle, with Wei's elite forces exhausted abroad and only the old and weak left guarding their capital. You should lead your army straight to Wei's capital, seize their key roads, and attack their vulnerable heart. When Wei sees their homeland in flames, they'll abandon Zhao and rush back to save themselves. This way, we lift the siege on Zhao in one move and crush the weary Wei army on their own turf."
Tian Ji followed Sun Bin's strategy to the letter, and everything unfolded exactly as Sun Bin had predicted: the Wei army, forced to withdraw from the besieged Zhao capital of Handan, turned back to rescue their homeland, only to find their retreat blocked by Qi forces and were compelled to engage in a hasty battle near Guiling. Having fought for days at Handan and then endured the exhausting march back, the Wei troops were utterly spent—how could they withstand the assault of the well-rested Qi army? The result was a decisive victory for Qi, crushing the Wei forces.
“Xing ge shi jin” — “ge” means “obstruct,” “jin” means “stop.” This idiom later describes a situation where the original circumstances are hindered and thus change.
Source: *Records of the Grand Historian*, "Biographies of Sun Tzu and Wu Qi"
Meaning of the Idiom: Later, the Chinese idiom "形格势禁" came to describe how the original circumstances are hindered and thus change.