As someone who also likes lists and organization let me offer a suggestion. When you have a plan outlined you obviously made it with some thought and you probably made sure it was optimal given what you knew at the time, and so naturally you are in some sense committed to seeing it through because you feel it should be done (or that this is the best way to do it). So when you are at step c and something gets in the way, it may feel that if things get done out of order it might not be as right. One way out of this is to realize that the plan was made in a moment which was past. In that moment you had a strategy, which got you to the present moment, where things are different. Now that you are here, you may need to re-evaluate and choose a different strategy. It's not that the original plan was wrong, but it was optimal for its time, and the world has changed.

So now you are a person 2 weeks into your A-Z plan, and you are stuck at C. But from another point of view, you are a person who has already accomplished certain things, and now wants to get to Z. Where do you start? What new possibilities has the moment opened up?

In sum, I suggest that when you feel stuck, say to yourself: "Paradigm shift!" and try to find the most interesting new way of going forward.

A last piece of advice, it's really all in how you narrativize it. You want to get out of the micro-stuck moments you describe, but also the meta-stuck moments of feeling the world is thwarting your well-laid plans. How do you learn to make ordered, organized progress without controlling things, or enforcing blinders? That's a harder question...