He Zhiling lost because he lost his nerve during the duel.
As the saying goes, when two meet on a narrow path, the braver one prevails. He Zhiling only knew how to turtle up and defend, never trying to attack. This allowed Zhou Fang to attack without restraint, completely letting loose.
As one's strength waned and the other's grew, how could He Zhiling possibly avoid defeat?
If He Zhiling had possessed even a shred of fighting spirit, daring to trade blow for blow in a life-or-death struggle, Zhou Fang might still have won, but not so easily. He certainly wouldn't have severed He Zhiling's arm without suffering a scratch himself.
This was especially true for the final move. Zhou Fang had thrust his sword straight for He Zhiling's throat. According to the standard principles of offense and defense in the Martial Dao, He Zhiling shouldn't have brought his saber back to defend himself, because at his speed, he couldn't possibly succeed.
