When I think of how I've messed up in attempts to consider the opposite, I can remember several instances when my tone was dutiful. I felt like I was supposed to consider the opinion that I disagreed with or didn't want to have turn out to be true. And yet, it felt boring or like submitting or something like that to really take that perspective seriously. I felt like I was considering the opposite roughly the same way a young child replies to their parent saying "Now say that you're sorry" with an almost sarcastic "I'm sorry."

A key thing here seems to be that if you really care about the getting right outcome, or in Eliezer's words, have Something to Protect, then considering the opposite won't feel like an annoying duty. Rather, then changing your mind will become something that you actually want to do.

Crucial Conversations is sold as a book for handling social conflicts, but you can also read it as a general rationality guide; in particular, it has a whole chapter on "how to stay focused on what you really want", which has this great example:

To see how the desires of our hearts can affect our ability to stay in dialogue, let’s take a look at a real-life example. Greta, the CEO of a midsized corporation, is two hours into a rather tense meeting with her top leaders. For the past six months, she has been on a personal campaign to reduce costs. Little has been accomplished to date, so Greta calls the meeting. Surely people will tell her why they haven’t started cutting costs. After all, she has taken great pains to foster candor.

Greta has just opened the meeting to questions when a manager haltingly rises to his feet, fidgets, stares at the floor, and then nervously asks if he can ask a very tough question. The way the fellow emphasizes the word very makes it sound as if he’s about to accuse Greta of kidnapping the Lindbergh baby.

The frightened manager continues.

“Greta, you’ve been at us for six months to find ways to cut costs. I’d be lying if I said that we’ve given you much more than a lukewarm response. If you don’t mind, I’d like to tell you about one thing that’s making it tough for us to push for cost cuts.”

“Great. Fire away,” Greta says as she smiles in response.

“Well, while you’ve been asking us to use both sides of our paper and forgo improvements, you’re having a second office built.”

Greta freezes and turns bright red. Everyone looks to see what will happen next. The manager plunges on ahead.

“The rumor is that the furniture alone will cost $ 150,000. Is that right?” [...]

As we watch Greta, something quite subtle and yet very important takes place. It is lost on most of the people in the room— but with our front-row seat, it is practically palpable. Greta’s jaw tightens. She leans forward and grips the left side of the rostrum hard enough that her knuckles turn white. She lifts her right hand, with the finger pointing at the questioner like a loaded weapon. She hasn’t said anything yet, but it is clear where Greta is heading. Her motive has clearly changed from making the right choice to something far less noble.

Like most of us in similar circumstances, Greta is no longer focused on cost-cutting. Her attention is now turned to staff-cutting— beginning with one particular staff member. [...]

In reality, Greta didn’t give in to her raging desire to defend herself. Almost as soon as her finger rose like a loaded pistol, it dropped back to her side. Her face relaxed. At first she looked surprised, embarrassed, and maybe even a little upset. But then she took a deep breath and said: “You know what? We need to talk about this. I’m glad you asked the question. Thank you for taking that risk. I appreciate the trust it shows in me.” [...]

Later that day we asked Greta about that transformation. We wanted to know exactly what had been going on in her head. What had helped her move from embarrassment and anger to gratitude?

“It was easy,” Greta explained. “At first I did feel attacked, and I wanted to strike back. To be honest, I wanted to put that guy in his place. He was accusing me in public, and he was wrong.”

“And then it struck me,” she continued. “Despite the fact that I had 400 eyeballs pinned to me, a rather important question hit me like a ton of bricks: ‘What do I really want here?’”

Asking this question had a powerful effect on Greta’s thinking. As she focused on this far more important question, she quickly realized that her goal was to encourage these 200 managers to embrace the cost-reduction efforts— and to thereby influence thousands of others to do the same.

As Greta contemplated this goal, she realized that the biggest barrier she faced was the widespread belief that she was a hypocrite. On the one hand, she was calling for others to sacrifice. On the other, she appeared to be spending discretionary funds for her own comfort. It was at that moment that she was no longer ashamed or angry, but grateful. Interestingly, by transforming her motives Greta simultaneously transformed the way she saw the man who asked the question. Whereas seconds earlier he looked like an enemy, when her motives changed, the fellow now looked like an ally. In fact, this man had just handed her the best chance she could get to influence the audience by letting her publicly address a primary source of resistance to the cost-cutting effort. And so Greta moved to dialogue.

Greta taught us that a small, mental intervention— the simple act of asking a potent question— can have a powerful effect on redirecting our hearts.

You're not talking about defending yourself about an explicit social attack, like the Greta example is; but the mental motion involved is similar: "ugh, why do I have to deal with this?". The subordinate's question, or the need to consider the opposite, is perceived as an annoying external force on you that you're forced to deal with.

I hadn't explicitly thought about it in terms of posture before, but the analogy makes sense. There's something that takes you out of the truth-seeking posture; and then to fix that, to return yourself to the right posture, you ask yourself, "what do I really want here?", or "what if I'm wrong?", and then you go back. (In the Greta examples, her change in mindset is even observable from her physical stance!) And for as long as you're in the non-truth-seeking mode, for as long as you are only interested in defending yourself or your actions, you'll be less flexible in terms of what you can do.