Developing that skill is really hard. It isn't the methodology. It's that you need the pervasive paranoiac scientific desire to poke holes in the idea. And that's very hard for most people. Carmack applies evidence to develop his posteriors very well.
i.e. when evidence comes along for an idea you have, most people will say to themselves "Even though that's true it's not enough" or "but that doesn't disprove it". In fact, I'd hypothesize (with poor evidence) that people who do not alter their posteriors when presented with evidence cannot do this at all. And that's very common - because lots of evidence won't disprove anything, it'll only make it less likely. If you never alter your posteriors you will dismiss it.
I know I sometimes fall in love with an idea and this happens.
i.e. when evidence comes along for an idea you have, most people will say to themselves "Even though that's true it's not enough" or "but that doesn't disprove it". In fact, I'd hypothesize (with poor evidence) that people who do not alter their posteriors when presented with evidence cannot do this at all. And that's very common - because lots of evidence won't disprove anything, it'll only make it less likely. If you never alter your posteriors you will dismiss it.
I know I sometimes fall in love with an idea and this happens.
By the way, here's a quick read of the idea if you can't read the video: https://amasad.me/carmack