Perceptions of honor can cause illogical reactions.

China has stated time and again that they'll not let Taiwan go. If Taiwan does declare independance, it'll force China's hand.

Either they do nothing and, even if it's just to themselves, be shown as weak-willed to the global community and lose face. Or they act to prevent it even though they know it's a no-win situation with a vast potential for negative PR.

Another option is Taiwan doesn't delcare independance, but works with China until at some point in the future, there's a good-willed parting of ways.