At the most critical moment, just as the nine Blood Beads were cracking and about to explode, Yusuf Zuck stuffed the last Golden Core into his mouth.
The Golden Core is a product born of tribulation; it's well-known that in order to achieve the Golden Core, one must endure a kind of heavenly tribulation. Cultivators refer to this heavenly tribulation as the Four Nine Heavenly Tribulation, a kind of mandated ordeal. If you can overcome this ordeal, you can solidify the pill; if you fail, you die.
This is why it is called the Four Nine Heavenly Tribulation—because at that time, thirty-six heavenly punishments will appear, and thirty-six is referred to as "Four Nine."
This is also the first ordeal that seekers of the Dao must face, and it is said that as one progresses, the number of tribulations increases.