Ok so for context, I definitely agree that in practice, in many cases it's not feasible to completely derisk openness from vulnerability, and often this means that the risk is totally worth it.
That said, I'm saying that the vulnerability itself, the harm risk exposure, is bad. So for example this could recommend noticing the exposure and studying it and sometimes marginally decreasing it, even as you're still taking it on, if you can't get rid of it entirely without also jettisoning some other precious stuff.
we are risking the comforting belief that we understand something or are justified in our actions
In this example, I would in real life become genuinely curious as to why the belief is comforting, in what manner it is comforting, what would be potentially harmful about having the belief contradicted, and how to avoid that harm.
One example is cognitive miserliness: rethinking things takes energy, so by default we avoid it. This is not a mere flaw! It's an important and useful cognitive instinct. If I'm going to override that instinct, I'd rather at least be aware that I'm doing that; and even better would be to check in with myself about whether I want to spend the energy to rethink things right now--sometimes I don't! And sometimes I do, and after I genuinely check in with myself and get a "yes", it feels less bad / harmful to get the belief update!
Another example is bucket errors. I don't want to answer someone's question if, by their psychology, I'm also accidentally answering "can I pursue my dreams of being a writer or not"! Unless of course tying my answer to the question to that other question actually makes sense. But often we tie things in way that doesn't make sense, or at least, in a way where you could do better if you thought about it more and debucketed somewhat.
(2) to show you that you're important to me in a way that I'm not incentivized to fake, and (3) to show you that I am the sort of person who cares about more than just my own perspective.
In my idioculture, these descriptions are ambiguous between intentions I would consider good and intentions I would consider bad. Roughly, I'd say it's very important that the action is good / makes sense / is healthy / is wholesome on the concrete object level, without the signaling stuff, in order to be a good signal. Otherwise what you're actually signaling is stuff like "I'll do needless damage to myself for the sake of this relationship", which, I don't mean to just generally derogate that stance because it sounds like it might come from deep love / devotion / need / other important things, but also I would say that it's not in fact healthy, and is not good for you or for the other person (on the assumption that the other person is a good person; if they are not a good person, they might enjoy or even specifically target that sort of self-damage).
But this person wouldn't be able to make costly signals to demonstrate genuine social connection.
I think this is totally deeply incorrect. You can simply invest your efforts to help the other person in a healthy way. Another way is trusting / relying on the other person, including in exposure to risk of harm, when that exposure is required by the task. For example, rock climbing with ropes where you rely on your belayer. Or starting a company, raising a child, etc. There's a ton of challenges that are worthwhile, and which often demand that we rely on each other including re/ risk of harm.
What blocks people from being vulnerable with others?
Much ink has been spilled on two classes of answers to this question:
There are a lot of people for whom these answers provide the right frame for their problems. This post is not for those people.
I want to focus on a different frame: there are importantly different kinds of things which people are hesitant to expose to others. Some of those things just require finding the right person and being vulnerable with them; these are the “easy cases”, in this frame. But other things pose fundamental difficulties, even when everybody involved has the safe-to-be-vulnerable-around skillset and isn’t particularly traumatized.
Let’s start with an easy example: sex stuff. Fetishes, sluttiness, that sort of thing. Revealing one’s sexual tastes involves being emotionally vulnerable. Moreso the more taboo one’s tastes are, with pedophilia on one end of the spectrum and anything in Fifty Shades of Gray on the other end. I call this an “easy example” because one’s sexual tastes are generally not inherently bad, and in almost all cases there are counterparties who will actively enjoy one’s own tastes. (... Though admittedly pedophiles have it particularly tough on that dimension.) The problem is usually just to find someone with complementary tastes, and then you can be in that wonderful world where someone not only accepts your deep secrets but actively wants you for them.
Now let’s contrast that with a hard example: suppressed temper. (In particular, suppressed PMS is what I’m picturing here, but the point generalizes to other kinds of suppressed temper.) Plenty of people have a temper, they often just want to scream at someone, but day-to-day they keep a mask over it. Taking that mask off involves being emotionally vulnerable. It feels good to have a partner who you can safely let loose at, knowing that you’re safe to do so - i.e. the partner can handle your temper (especially when it’s directed at them) and won’t be driven away by it.
But in contrast to the sex case, basically nobody likes being berated. Being emotionally vulnerable by letting your temper loose will be costly to your partner. Hopefully the relationship can be net positive for both people anyway, but there’s no avoiding that this kind of emotional vulnerability hurts the counterparty, even if their skin is thick enough for the hurt to be mild.
That’s what I’d call a “hard case”, in this frame: a case where you usually keep something hidden from people because exposing it would hurt the people exposed.
What can we do, in the hard cases, to make things work well?
I don’t have general answers, but I’d like to hear what answers other people have.