Any nontrivial component, which today does whatever its job is today, but is very brittle and resistant to change and is centrally located in the overall system

Any nontrivial component, which today does whatever its job is today, but is very brittle and resistant to change and is centrally located in the overall system architecture/structure, certainly can become tomorrow's untouchable 20 k LOC VB.net script. Having something like that is like a pressure point for business risk. A small nudge here, and the whole shaky house of cards violently implodes ejecting all kinds of badness, monetary and otherwise, over those around it. And it is not just the bad component, it is the overall system design which permits this and does not support change within the system ("modifiability", "extensibility", ...). Point: it is not as easy as saying "oh, this is because of that incompetent asshat". The incompetent asshattery is a systemic phenomenon with many actors. Death by a thousand small bad choices; the 20 LOC of untouchable code is just a manifestation of the bigger problems.