Thinking about this, what are we discussing really? In any writing, the writer should be trying to surprise the reader. It's the essence of a page turner. Question > answer > question > answer and so forth. The answer can either be a mystery solved, a conundrum resolved or an unexpected tangent/twist.
I think for this to not get in the weeds, a specific definition needs to be established. I personally, when I first saw the thread, thought it was about 'twist' endings, which are great but often overused and seldom subtle. Discussing what makes them subtle would then focus the discussion specifically and stop it getting in the weeds.
A good idea, though I was planning on saying the opposite. The discussion is focusing on the big surprises, or mysteries. My style of writing is to, as much as possible, put in little surprises. I think there is a flow to writing, a direction, but I turn that off for something the character does that might be unexpected. We should talk about the techniques for doing that.
I'm thinking surprise with insight, surprise with delight, surprise with disgust, surprise with pathos. Like it's salt or sugar and can be added to anything.
He has a house, a dog, a toaster, and a level of maturity I suspect I haven't yet obtained. (TrickyTwenty-Two,Evanovich)