Besides being highly skilled in medicine, Xue Zhiyi was also an expert in poison-making, which was why the Empress Dowager sought him out.
This was also the most regretful thing he had done in his life; he believed that An Ping's death was a retribution for his poisoning others.
Since then, he never made poison again and gave up his medical practice, moving to the mountain to become an outlaw.
However, he unexpectedly encountered the Second-in-Command and his group on the mountain, who seemed to be avoiding something and accidentally intruded on his territory. He initially wanted them to leave but unexpectedly discovered that they were poisoned. Coincidentally, the poison was one he had created. He mocked himself for wondering how many people he would end up harming.
So he gave them the antidote and let them stay on the mountain.
