but in my writing experience, there hasn't been a correlation to high levels of canon certainty about the relationship. High levels of emotional importance to the characters are a factor, though...

Yeah, I think I'm expressing the "canon certainty" thing badly. I was trying to get at "because of how things go in canon, I'm pretty confident that they will get together and stay together, in a relatively stable relationship." As opposed to two guys who meet twice in canon but somehow spark like fireworks in fic. But I have tiny sample sizes, and that factor may be more correlation than causation.

Both Zhao Yunlan and Shen Wei are complex people, and their relationship - as unquestioned and soul-deep as it is - is even more complex, with steep differences in knowledge and secrets and other such impediments littering the emotional landscape.

I don't think it's about complexity for me. I had an RPS pairing for a while that were a complex mass of all kinds of interdependencies and issues, and they were wonderfully filthy. And I had a similar smutblock (though to a lesser extent) with Fraser/Kowalski in Due South, and their relationship was actually pretty straightforward.

But in the instance of Guardian, I think you're right -- those high stakes and the care they take definitely exacerbate the problem.

Ooh, maybe it's simply how careful they are of each other? Hmm... *continues to ponder*