There was a Lost You Forever symposium held on 8 Aug 2024 in Beijing where leaders, industry experts, scholars and representatives of key creators conducted in-depth discussions and professional interpretations of 'Lost You Forever' from various angles.
During the LYF symposium, Tong Hua provides her explanation for why Cang Xuan's character arc deviated from the novel:
Let me use an example to share with everyone. For example, my (understanding) of the main character Cang Xuan. When I was writing the novel, my understanding at the time was that I felt that during the later part of his journey, actually, in a certain sense, he himself had lost his own self due to power, which was why towards the later part, he took measures to assassinate Tushan Jing. I felt that this was an indication that as he continued step by step (down that path), he himself had also forgotten his original intentions and aspirations. However, in the end when I went back to write this character once more, because many of his hidden lines - his friendship with those beside him, his familial ties, including the companionship of those minor characters beside him - I myself felt that my understanding of this character has deviated in some way from in the novel. When I wrote the script, I would feel that he had undergone so much, so instead, I felt that he could overcome what came with power. That is he didn't [think that] - that is to say, you think you can do everything. Rather, he learnt to overcome, to overcome his own desires. Which is to let go of his personal love, lesser love, and choose a more magmanimous love to fulfil [the wishes of] others. In fact, in some sense, when you fulfil others, you are also fulfilling yourself at the same time.
-- Tong Hua interview 8 Aug 2024, LYF Symposium - regarding changes to Cang Xuan
cr. Weibo source