This study will explain Koguryo’s war with Sui from the perspective of the puzzle of weaker actor victory in asymmetric warfare. The war was asymmetric in terms of relative material power, i.e., conventional military capabilities. In asymmetric warfare, superior leadership is vital for victory, and Koguryo’s King Yongyang showed this. Koguryoenjoyed success in the war, because it employed an effective military strategy in which it avoided direct warfare that played to Sui’s superior numbers and adopted indirect warfare designed to protract the war and wear down its enemy. The people of Koguryo were much more motivated to fight than their Chinese counterparts. Koguryo’s victory demonstrates that non-material factors are no less important than material factors in asymmetric warfare and that specifically superior strategy and strong resolve form the crucial factors for the weaker actor.