Everyone was looking at their own shoes
"It's just how I am"
The last belief that holds the audience in place is the flat one. This is how I am. I've always been like this. Some people feel watched and I'm one of them and there's no more to be said.
Some of that is fair, and I want to be honest about the end of the spectrum before I argue with the middle. Jane Spurr and Lusia Stopa reviewed the research in 2002 on what's called self-focused attention in social anxiety, using a model from David Clark and Adrian Wells. In that model, attention turned inward is a maintaining factor. It increases access to negative thoughts and feelings, gets in the way of doing the thing you're doing, and stops you seeing the external information that might contradict the fear. People at that end build a picture of how they look from inside, often as though seen from outside, and it's inaccurate. That's the clinical end, and if you recognised yourself in the preface's list, it's worth taking that seriously and reading chapter 23.
But look at what the model says the mechanism is. It's attention. Not a trait, not a type of person, but where attention goes in the room. Susan Bögels and Warren Mansell reviewed the same area in 2004 and found reasonable evidence for treatments that work directly on attention, along with a list of the mechanisms they thought responsible, of which reduced self-focused attention was one. They also said better-controlled studies were needed, and I'll leave the treatment claims there, because this isn't a treatment book. The point I'm taking is smaller. The thing that keeps the beam on is described, by people who study the hardest cases, as something that moves.
So the belief is half right. You do turn attention inward in rooms, and you've done it for years, and that's a fact about you. The other half, that it can't be otherwise, isn't what the research says, even at the severe end. And in the ordinary middle, where I'm assuming most readers are, attention moves with a nudge, which is what the shoe count is.