Qi Cultivation was all about refining a strand of Spiritual Energy into oneself, claiming it completely as one's own. Foundation Establishment was about solidifying mana within the physical body, completely transforming the mortal physique. Both of these changes only concerned the "self." During a Breakthrough, Spiritual Energy fluctuated, but no extraordinary phenomena manifested.
However, Golden Core Formation was different. Spiritual Essence hugged the core for sustenance, uniting inner and outer self, body and mind as one. According to the Ancient Method, this was the Unity of Heaven and Man. The Modern Cultivator saw this as the point where the mana circulation system shifted from a closed system to an open one. Upon the formation of the Golden Core, the winds and clouds stirred, and spirits wept. These phenomena occurred when the inner and outer systems of the Cultivator began to intersect and the circulation of Spiritual Energy was suddenly disrupted.
