I did debating in school and a lot of the prep was like this too — once you have your position sketched out, you put on your 'opposition hat' and start to critique your own position for holes.

Also, where in the HN guidelines it says — Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith. — when you're prepping, you tend to do just the opposite: assume that someone _is_ going to attempt to respond to a weaker version that's easier to criticize.

It can help you have a rebuttal on the ready if needed but regardless it also helps you to distill/reframe ideas in a way that's clearer from the outset (which is a good thing in & of itself, even if you don't have someone taking a counter position)