In this realm, everyone is born with spiritual veins. However, their purity and rarity is what determines whether or not an individual can cultivate.
Bloodline dictates this, however there are rare mutations where an individual is able to 'leap the dragon gate' and become a cultivator.
Purity determines whether one can train or not. It also dictates how far an individual can go. Purity of a spiritual vein can be increased, however through painful and expensive measures.
Rarity involves the power output. The more rare the vein is, the more powerful an individual would be. Though, it is a double-edged sword; it also becomes much more harder to cultivate. There would also be more requirements to train.
Void Spirit Veins are one of the rarest spiritual veins. Thus, its requirements are one of the harshest.
And, fortunately (or unfortunately), the Wuxia Jin Yahui was gifted with a 99% purity and void spirit veins.
And our protagonist Jin Yahui will have to figure out the conditions for himself.