The complexity of getting different pieces to talk to each other? I can see how that's only conditionally "essential" in that, if you have enough control over the environment, you can make the various distributed components as similar as possible, never deal with version skew, and never deal with varying interpretations of the same protocol standard.
OTOH, if you're writing a web page, and you have to make that page useful across multiple browser types and versions, some way of dealing with the vagaries of different browser implementations becomes an essential complexity: You either push it into a library or framework or you handle it in the main codebase, but something has to know what MSIE can and cannot handle.
Further, there's different levels and causes of “coordination didn't happen”, such as “we tried, but got confused and didn't have time to understand each other properly” or “actively sabotaging everyone else's ability to deal with the aggregate system so that I can get ahead”… and somewhere in there is one that stands out to me as specifically interacting with technical complexity, along the lines of “I want my piece to not have to be the one that changes and/or takes on other costs”. Which is part of the social dynamic of moving externally-essential complexity around within the aggregate system and potentially creating ripples of accidental complexity along the way.
(Whether and how this also happens when the information systems in question are human minds rather than software components might be relevant but also an exercise for the reader…)