Yeah. As phrased it is bad advice - nobody actually needs to be "vulnerable". Everyone should be in a headspace where they might actually change their mind rather than persuade the counterparty, which feels like vulnerability to people who define themselves by their own beliefs. The trick is not to do that; a person isn't their beliefs. People have beliefs, but those can change. They're still a person both before and after the change (which sounds a bit ridiculous to have to say, but by observation some people don't seem to believe it to be true).
Some people are just too stubborn, especially if they come from a place of authority and seniority. I'm doing house repair work right now with an older relative. He learned how to do repairs and renovations by himself, things like working laminate floors, mortar, laying tiles etc. The things is, he has his own reasoning and rhythym of doing things and doesn't like to be challenged, but I feel his ways don't always make sense, esp when I feel he is rushing and improvising (a programmer can tell). I haven't done much handy work myself in the past, but I'm a millennial, so I google things, watch youtube videos, and I read instructions. I also know that it isn't rocket science, my parents built our own home brick by brick. And now, every step of the way I have to be pushy to get my way, and make it sound like I'm not imposing or too nitpicky or challenging his "expertise", it's very taxing, I made a big scene once already and the whole relationship is now strained.