Once again I've been thinking a little bit about how in a lot of places "vulnerability" and "openness" are conflated, while for me they're on a see-saw...
I.e. (for me) I don't feel very "vulnerable", I am confident in my ability to muddle through nearly anything, and so I'm willing to be "open" and talk about nearly everything, and be frank about how I feel about things. So the more vulnerable, the less open, and vice versa.
Hm. I guess it's because... well, maybe I feel things less, then? Or rather I'm less driven by my instinctual preferences than a lot of people. I know "I feel things less" sounds awful and robotic, but being able to have some say in what instinctive emotions seem likely to serve me -- which emotional interpretations are well-aligned with SHARED reality and so can be given room to grow from seedling to strong plant, vs what instinctive emotions don't seem in my best interest and should be broken up as a seed -- is good for me.
So I could imagine if I was less adept at curating emotions early, if my only option was to build a macho firewall facade around a raging flame of sadness or anger or whatever, then I would see how vulnerability and openness were more related. But I don't rage like that! (At least not often) And so I'm willing to talk about anything with great candor. (Though I think Joel's damning line to Clementine in Eternal Sunshine of the Spotless Mind - "Constantly talking isn't necessarily communicating.")
(I was thinking too about once place I might be very vulnerable - I'm compulsive about Not Being Wrong. I don't have to be Right, for sure, but I have to express my uncertainty in no uncertain terms. This can lead to me being less clear and hard to follow, like when I start off with the disclaimer: "i know their might be competing views of this, and here's what they are, but I think the correct view is _____". All the disclaimers are absolutely a defense mechanism for this core vulnerability - so maybe I'm less "open" in that way.)