People are not born with willpower. Although some people are born with stronger willpower, it could not be much stronger.
The true elites gained experience through repeated failures. It enabled their hearts to become stronger. The more times they failed, the stronger their hearts could become.
Of course, many people were not up for enduring such training. They easily gave up under the intense suffering repeated failures can bring. They would lose themselves and become the ones who never were special or anything big in life.
Han Sen had encountered constant troubles. It was unknown how many times he had almost died. He had succeeded a lot and failed a lot. His heart had been trained through many crises. Although no one could say his willpower was more stable than the willpower of others, in this world, few things could truly move his will.
Although the sword shadow's willpower was stronger than his, it was unable to make Han Sen bend enough to break.