this is actually in the footnotes and addressed by the "thinking in bets" section
"[9] Fully understanding I can be the one in the wrong -- however, when this is the case, the person explaining is usually able to:
understand my argument convey their disagreement in good faith without circular reasoning or rhetorical tricks"
"There's a 40% chance this succeeds because of A, 25% chance of B, 10% of X, and 5% something we haven't thought of"
That's not what this is saying at all.
"Understand my argument" does not imply correctness in the slightest.
It's possible to understand an incorrect argument and show where it's going wrong, plenty of people can detect fallacies. I've both done it to others and had it done to me.
This seems to be a combining of "understanding" and "agreeing", which are separate things.
But you are the one both defending the argument and judging if they understood the argument.
If it is your argument, it means you believe in it, it means you think it is a good argument and not a bad argument. So maybe in fact they are right and they understood the argument correctly, but you are the one mistaken. How can you tell?
Let's, for the sake of discussion, imagine that your argument is bad. You believe it is good, but it is bad. It means that you don't yourself understand your own argument. How can you therefore judge if someone has understood the argument or not?
You were saying that you can see when they use "circular reasoning" and "rhetorical trick". That's exactly the first impression that everyone has when they defend a bad argument and someone points at the flaws in it.
I'm not mixing up "understanding" and "agreeing", I'm saying that you claim that you can tell if someone "understand", and I'm simply saying that it is not possible to tell if someone has understood if yourself you believe the argument is correct and they belief the argument is incorrect.
The footnote is basically saying "I can tell when it's the case or not", which is in fact exactly my problem. That is not the answer that I'm expecting from someone who has self-reflection.
For example: "understand my argument" is assuming that the argument is obviously correct. When someone presents to you an incorrect argument, 1) this person thinks the argument is correct (otherwise they will not present that argument), 2) you will not answer by saying "I've understood", you will argue. From their point of view, you are the one failing to understand. Now the question is: how many time this person was you? How many time you presented a bad argument and then blamed the interlocutor for "not understanding" when they don't accept a faulty argument?
Same with "circular reasoning or rhetorical trick": when I disagree, it is always very easy to convince myself that there is a problem in the interlocutor logic. Especially if I failed to understand or misunderstood the argument. I would even say that for all discussions that are not trivial, there are always elements that can be seen as circular or rhetorical trick.