Lengthy comment below. The application of social proof to my ex-coworker is at the end.

Social Proof is a concept in the book Influence by Cialdini. I strongly recommend the book - fairly entertaining.

The idea is that your brain relies on people you consider to be your peers/in-group for many things: customs, social norms, and even truth. Your brain usually looks to them for guidance on the above, and often ignores others.

This is why the Bystander Effect is particularly pernicious. When something horrible is going on, and you see your friends observing it and doing it, your brain is primed to say things "My friends accept this, so there's probably nothing wrong with this" or "My friends are not interfering. I probably shouldn't either" When someone does interject and help, it's often by someone who does not consider the other bystanders as part of his peer group. This is expanded on here: https://blog.nawaz.org/posts/2017/May/social-proof-and-the-b...

I often deal with this at work. I've had fellow coworkers make a claim, and I show a (simple) mathematical proof disproving their claim. The outcome is usually one of the following:

1. They accept they were wrong, but it doesn't stick in their mind. A week later they're parroting the same wrong thing.

2. They look at their peers in the room, and ask "Have any of you heard of this?" If no one has, they outright reject my proof without finding any flaws. This was shocking to me, but it's happened so often at the workplace I find it normal now.

I once got a bad rating at work because a particular circuit simulation wasn't behaving the way they expected it, and they insisted I was either running it wrong or had messed up the circuit file. I hadn't. I asked why they expected it to behave differently. The answer was always "We've been doing this for over a decade and the capacitance is never sensitive to the following inputs." This was tribal knowledge and I was the lone person questioning it.

The circuits expert was on vacation. The work stalled for 2 weeks where I pretended to find the flaw, and had to answer daily that I hadn't found it. Upon the expert's return, I go to him and he sends out an email to all of them saying "Your beliefs are wrong. The capacitance can change with those inputs. There's nothing wrong with the simulation."

But the damage was done. I was still viewed negatively. And I'm sure if I ask them now, they'll go back to "the capacitance never changes with those inputs" - it's what everyone else believes around them.

I've seen this in the SW world as well. Actually, much more often. Avoid a quicksort injection attack by randomizing the list (O(N) operation) first, and a room full of programmers laughed at me saying "That's silly! We're trying to sort a list and you're jumbling it up first. That's just going to make sorting harder!" (And no, they did not have an alternate solution to the attack).

I thought I was immune to such behavior. Surely, if someone comes to me with objective advice/evidence, I'll listen to him! But after I read that book, and as I got older, I encountered a number of situations where I was in the wrong, and realized that at some point in the past I had been advised on the correct path, but did not take it. Why did I not take it? The answer was always social proof: The person was not in my peer group, and so my brain always had an excuse. That person doesn't understand my perspective. Or That person lives a very different life. I don't want to live his life.

Random example from HN: Go search for Sarno and his treatment for back pain. Read up on Sarno's views on what caused back pain (and some other pains). For someone like me, his theory and solution is very much nonsensical pseudoscience. Had most people come to me with it, I would have dismissed it. But here I was on HN, with a significant number of folks stating how their back pain was gone for good - at times after years of suffering - by following Sarno's advice.

This is my crowd[1], so suddenly I did consider reading up on it and applying it.[2]

Getting back to my ex-coworker. He came from a culture of extreme competence. Very good at math, physics, and programming. Knew the low level details really well. This was considered a bare minimum to graduate from his elite university (not in the US). He felt all universities should have those minimum requirements, and since they didn't, someone had to protect teams at the company from them. He couldn't control hiring, but could control quality within the team.

By having that world view, he had automatically made all his teammates be part of the out-group. They were not his peers, and so he would ignore any advice they could give. Hence, no one was in a situation to gently steer him to better behavior.

[1] A tell tale sign of social proof in action is when someone says "I know it sounds crazy, but you should listen to this guy. He's one of us.

[2] Sorry for the non-spoiler. His advice didn't help me with my pain. But I totally accept it did for others, and do suggest it to others.