"If I sound unsure, nobody will listen"

Some people hold because they think confidence is what gets them heard. In a meeting where everyone's certain, the person who says "I might have that wrong" gets talked over. So you keep the certainty up, even after the turn, because dropping it would be dropping out of the conversation.

There's a study that complicates this. Uma Karmarkar and Zakary Tormala ran three experiments in 2010 on how the certainty a speaker expresses affects whether people are persuaded, and found that it depended on whether the speaker was seen as knowing what they were talking about. Speakers seen as having no particular expertise were more persuasive when they sounded certain. Speakers seen as experts were more persuasive when they expressed some uncertainty. The researchers' explanation is that each combination is a small surprise, and the surprise makes people pay attention. An expert who says "I'm not sure" is interesting. An expert who's certain about everything is furniture.

That was consumer research, with product reviews, and I'm carrying it further than it was tested, so treat what follows as my reading. In most of the rooms where you're holding, you're the expert, in the sense that matters. It's your area, or your family, or your project, and people already credit you with knowing things. For that person, certainty is expected and adds nothing. Uncertainty said out loud, "actually, I'm not sure that's right any more," is the thing that makes people look up.

There's a longer game here too. Certainty is a currency and you spend it every time you use it. If you're certain about the roundabout and the supplier and the film, and you're wrong about the roundabout and hold anyway, your certainty about the supplier is worth less next week, because people have seen what it's backed by. If you're certain about the supplier and say "I'm not sure" about the roundabout, the certainty about the supplier is worth more, because they've seen that you hand it out selectively.

The person who is never unsure isn't listened to more. They're discounted, quietly, by everyone who's noticed that their certainty doesn't track anything.