I'm working on a roadmap of ideas covered in the Sequences and related comments & posts, and I find it peculiar that Preface has inspired you to write regularly. It haven't crossed my mind at all while I reread the Preface thrice – cannot agree more that good ideas must be shared with others.

However, it's sad to see that your challenge has ended abruptly. Would you mind writing a postmortem? 

I believe that PCK itself is incredibly helpful, but, unfortunately, there isn't much material on how to actually use this technique as a self-learner when there's no teacher around to be curious about your mistakes and guide your way through your subject of choice.

I fully agree with the idea to be kind to yourself and reflect on what exactly went wrong in your line of thought instead of blaming yourself for errors, but sometimes you just get stuck at some point: you know that something isn't right, but you don't know what exactly even when you can fully recall what you were doing, so you can't define the mistake without help and, consequently, fix it. In my opinion, such situations can be crucially demotivating, and I wonder whether there's a way to use PCK more effectively aside from making self-reflection a habit.