You are not getting the point of either my comment or the original article. You are thinking from an engineering point of view, where if you look through all the layers of abstraction you see mutexes and shared mutable memory. That's not my point; my point is about building up those abstractions so they are sufficiently hidden. Functional programmers routinely operate on a higher level of abstraction, and they have shorter, more maintainable code. In such code, it would be a code smell if you continue to use mutexes, because that should've been an implementation detail. It should've been clear from the outset that the kind of complexity the article is talking about is cognitive complexity.