There is an art to presenting vulnerability; to not diminish yourself whilst doing so. It not only improves your own outlook on yourself but helps prevent others using it against you, all whilst still being open and truthful.
Its hard.
Its hard.
But when something happens that contradicts your model, it means your model is wrong, and this causes severe anxiety (cognitive dissonance). This explains why people get more upset when things don't go the way they expect than whether or not things go badly or well, which is why managing expectations is such a high priority for project managers. It also explains why autistic people who struggle to abstract and get upset by social disappointment rock themselves: to create a signal they can predict. Otherwise, the bottom of your world falls out every time someone moves their cheese - like a baby throwing a tantrum when they drop their favourite toy before they have a model of gravity.
Now, why would people want to get drunk together? I think we want to test congruence and resilience in a vulnerable situation. The better a person can predict your social cooperation in a variety of contexts, the less bandwidth they can afford to devote to modelling your actions, which might otherwise pose an existential threat. Once you have mutually compatible models of cooperation, you can safely turn your backs to each other and work on solving external problems without causing internal anxiety.
But being predictable also means you are vulnerable. If you can be modelled, you can be manipulated. So we crave a certain "predictable chaos" from our friends, partners and co-workers. We want someone self-aware enough to follow the rules, while pleasantly surprising us in ways that expand our mental territory without invalidating too much of the existing foundation. A quick way to upset a drinker is to turn down free drinks at a bar at night (but not in the middle of the day). It forces them to re-evaluate their model of the world - and, people hate doing that, especially drunk people. The same is true of questioning people's religion.
Incidentally, this is also why you dream and have nightmares, and seek out horror movies when things feel stagnant. Your mind is exploring your survivability in a bunch of threatening situations that could arise, and learning from them without dying.
Incidentally, the essence of what you say (the mind is always predicting and learns from prediction failure) is also the essence of idealist philosophy, and has found its most advanced expression in Kant's Critique of Pure Reason. Unfortunately, Kant uses a language that's difficult to access today, so a lot Kant's insight has fallen out of today.
The most popular trust-creation mechanism for adults seems to be getting drunk together, which reliably leads to little infractions, which every witness has the choice to exploit or not. The latter option engenders trust.
"I don't trust someone that I didn't get drunk with" is a sentiment I've heard repeatedly, both privately and professionally. The most successful startup that I worked for even asked "What's your favourite beer?" when they interviewed me for a programmer position, and when I asked by this was of interest, they said they took their after work drinking sessions pretty seriously, and "don't want to work with people they can't have fun with". As somebody who doesn't enjoy being drunk, this was difficult for me to adapt to.
As to the drinking after work... I think it's appropriate to set boundaries. I only drink a handful of times a year but will participate in some activities including outside work hours, I also don't have more than a single drink if I'm going to drive within a couple hours. Also, get two non-alcoholic drinks or glasses of water per alcoholic beverage, could pretty much stay close to sober all evening when I was in my 20s by doing that.
In the end, it's about striking a balance of being sociable without being irresponsible at the same time.
Note also that pretending to drink feels a bit like cheating to me: I'm actively deceiving others. I wish I could live my life without deceit.
That's something I've heard as well, and I tell them that drinking with me is a bad idea, and getting me drunk is even worse. Because that's when my persona slips and my shadow comes out to play -- and my shadow is kinda like Sam Kinison, only not funny.