"Complexity fog" is where uncertainty occurs during highly complex debate, operations or meetings. The term seeks to capture the uncertainty regarding one's own capability, our adversary capability, or the adversaries intent.
It is a paradox. The more we are certain about and know, the less we know and are certain about. Simplicity just allows you to have a perception that it is clear.
Individually we can increase our threshold to "complexity fog" through education, training and useful frameworks. The purpose of peak paradox is to provide such a framework to enable individual leaders and executives to see clearly in highly complex situations.
I would like to link complexity fog to the concept of the Fog of War: https://en.wikipedia.org/wiki/Fog_of_war as I believe the dynamics resonate well :-)