Changing your mind out loud
The third part is for the bigger turns, the ones where you'd argued a position for a while, or in front of people, or at work, and five words isn't quite enough because people want to know what happened. This is the climb-down with its reason attached, and it's the version chapter 8 promised, the one that makes a change of mind look like what it is rather than like a weathervane.
Three sentences. What you thought. What changed. What you think now. "I said the new supplier would be cheaper. I've seen the onboarding figures and they take it over the old one. I think we should stay where we are." That's the whole thing, and none of it needs a fourth sentence. The middle one is the important one, because the reason is the difference between changing your mind and just changing sides. If there's no reason, you're not ready to say it yet, and "I'm not sure any more" from chapter 15 is the honest placeholder.
When. As soon as you have the reason, and in the same room if you can. Within the hour is better than within the day, and within the day is much better than within the week. A late climb-down is still worth doing, and chapter 25 is about that, but each day it waits, the slide sets a little harder, and people have started to plan around your line.
Where. In front of the same people who heard the line. If you argued for the supplier in the meeting, the change of mind goes in the meeting, or in the same thread, not in a quiet word with one person afterwards. The audience that heard the line is the audience that needs to hear the reason, and telling one of them privately is the slide with a witness.
Thank the person if it fits. "Thanks for bringing the figures" is worth saying, once, plainly, if someone brought you the thing that changed your mind. It costs nothing and it's the most direct way to make sure they bring the next thing. Don't overdo it. One sentence. Chapter 19 described what happens to the corrections when correcting you is expensive, and this is what makes it cheap.
What it isn't. It isn't a speech about how you value being challenged, or a reflection on your own openness. Those are about you and they're a way of making the climb-down into a performance, which is the salvage in a better suit. Three sentences. What you thought, what changed, what you think now. Then the meeting moves on, which is the whole point.