After the old emperor of Western Chu died, Xiang Yuan first sought out Palace Lord Bai, then Que Xin, and learned of the Book of Life and Death—as well as the method to break it: the Three Yin Book of Life and Death plus the Ancient Mirror of Reincarnation.
To prevent the mastermind behind the scenes from striking again, he traveled through many regions and, before the Book of Life and Death could act, cursed Liu Che and Xiao Yan first.
Over at the Southern Jin imperial court, he ran into a neither-hard-nor-soft nail.
Grandmaster Li Yuanrong of the Shangyuan Li Clan was willing to trust Xiang Yuan, but Southern Jin's old emperor hesitated greatly. The method for breaking the curse was to be cursed by Xiang Yuan; no matter what, one's life would be placed in an outsider's hands. After pondering for a moment, he ultimately refused.
It was understandable. Xiao Yan saw Xiang Yuan as his adopted son plus son-in-law times two, while Liu Che saw him as the troublesome senior brother from True Heart Dao. Disdain was disdain, but the trust that should have been there was not lacking in the slightest.
Southern Jin's old emperor did not dare trust Xiang Yuan lightly, much less gamble on him. Even Li Yuanrong's guarantee at his side was useless.
What you said makes perfect sense, but how do you prove this fellow surnamed Xiang isn't the mastermind behind it all?
Look, he even has the method to break it!
In the end, Xiang Yuan failed to cast the Life-Death Reincarnation Curse on Southern Jin's old emperor. But the old emperor did not dare put all his eggs in one basket either, so he put forward three princes and had Xiang Yuan curse them.
Now, the old emperor was dead.