I think of "invisibility" as a way of removing unnecessary friction and the author doesn't quite drive home that point effectively.

Good invisibility is like well designed roads. Smooth, clear markings, adequately wide or narrow for the desired speed, easy and obvious signs. Unbothersome and pleasant. Drivers simply drive, rather than get bothered by, "gotta avoid the pothole. Here's comes the bumpy part. That blindspot, I gotta slow down for way too much. Unseen pedestrians pop out here."

This is where invisibility in interstate highway regulations are obvious.

When I see TUI vs GUI comparisons, it distills to friction for a given context/workflow.

I worked in a restaurant with a micros system. It was a very easy to use GUI that was touch screen button driven. A 1 person order could easily be entered in 6-7 button pushes in 2-3 seconds to a seasoned operator: drink > coke > dish > steak > medium > a1 > submit

The beauty with micros was that it reduced the typical navigate > select > add > back-to-navigate workflow into 1-2 button presses with a receipt-like tally providing immediate state feedback.

In this scenario, telling a user to get into a terminal console and type "cd Foo; ./add ketchup" would violate the invisibility principle. It has nothing to do with TUI or GUI.

To me, good tools get out of the way, in the given context. Micros did that.

CLI users are in a CLI flow, thus introducing a mouse to a keyboard workflow violates the invisibility workflow. But for a GUI user to hit up the terminal violates their flow.

Ultimately, all workflows are in search of a faster/less-toilsome feedback loop to the desired goal and tools are in service to the loop. Well designed tools with rabid followings understand through usage where to add friction, and where to cut toil and I'd argue this is where CLIs shine with decades of refinement of the same tool chain.

GUIs are a, it depends on how composable or self contained the given problem for a GUI interface is.

But yes, tools should be invisible. How they become invisible depends.