Cognitive load is what matters

I think it's pretty tiresome that "smart authors" are blamed for writing complex code. Smart authors generally write simpler code. It's much harder to write simple code than complex for reasons that boil down to entropy -- there are simply many more ways to write complex code than simple code, and finding one of the simple expressions of program logic requires both smarts and a modicum of experience.

If you try to do it algorithmically, you arguably won't find a simple expression. It's often glossed over how readability in one axis can drive complexities along another axis, especially when composing code into bite-size readable chunks the actual logic easily gets smeared across many (sometimes dozens) of different functions, making it very hard to figure out what it actually does, even though all the functions check all the boxes for readability, having a single responsibility, etc.

E.g. is userAuthorized(request) is true but why is it true? Well because usernamePresent(request) is true and passwordCorrect(user) is true, both of which also decompose into multiple functions and conditions. It's often a smaller cognitive load to just have all that logic in one place, even if it's not the local optimum of readability it may be the global one because needing to constantly skip between methods or modules to figure out what is happening is also incredibly taxing.

I like to call that a leaky abstraction. The author used "UNIX I/O" as a great example. It perfectly hides the complexity and abstraction is such a way that the programmer never needs to know the internals. It has sealed all the juicy complexity in a watertight container that the user of the abstraction never needs to peak inside of.

The auth example may not be. You may need to do validatePassword(user) for passwordCorrect(user) to be true, which then forces you to open up a hole in the abstraction that is userAuthorized(request) and peak inside. userAuthorized() has leaked out its logic, it has failed as an abstraction. Its a box with 3 walls and no roof that blocks visibility to important logic rather than hides away the complexity.