Logically speaking, helping someone to break through to the next Golden Core Rank, a task that requires the seemingly trivial or even unnecessary "Primordial Yin," should be something no one would refuse.
Between the middle and higher ranks of Golden Core, there is an invisible chasm called "cultivation talent." It solidifies from the moment of birth; one either has it or does not, with typically no way to change it.
Now, over this insurmountable chasm, someone has suddenly erected a narrow bridge.
Most cultivators would go to all lengths to cross this bridge. Let alone Primordial Yin, even if it meant self-mutilation, or enduring severe pain, there would still be plenty willing to take the plunge.
