"Why?" Yan Yu pondered for a while, "Because it produces Yin Dregs?"
"Exactly." Sword Intent said indifferently, "Cultivation is not only about accumulating mana but also about refining the Yin Dregs in the Primordial Spirit. Why do cultivators of the Xuanmen Zhengzong, before Core Formation, often need to cultivate for two or three 60-year cycles, waiting until their lifespans are nearly exhausted to Cross Tribulation? It is to eliminate as much Yin Dregs as possible, making their Purple Mansion Foundation purer."
