Putting content in the right order and hitting the right abstraction level.

Keeping the reader/user in the zone between being bored and overwhelmed while you teaching them, without knowing something about them (only data as feedback if they are using a tool that you built,rather than them raising eyebrows or nodding in a classroom).

I think it's hard but also fun. For the EV stuff that I look at there are a few problems compounding this:

+ Overwhelming buzzwords and complexity

+ Wrong intuition for HV systems

+ Unclear where to start

+ Capital requirements are high

+ Dangerous tech