Largely as a consequence of their complex and densely interwoven nature, in the event of a breakdown in ubiquitous systems, it may not be possible to figure out where something's gone wrong. Even expert technicians may find themselves unable to determine which component or subsystem is responsible for the default.
Let's consider the example of a "smart" household-management system, to which all of the local heating, lighting, ventilation, and plumbing infrastructure has been coupled. In the hope of striking a balance between comfort and economy, you've set its winter mode to lower any room's temperature to 60 degrees Fahrenheit when that room has been empty for ten minutes or more, but to maintain it at 68 otherwise.
When the heat fails to come on in one room or another, which of the interlinked systems involved has broken down? Is it a purely mechanical problem with the heater itself, the kind of thing you'd call a plumber for? Is it a hardware issuesay, a failure of the room's motion detector to properly register your presence? Maybe the management interface has locked up or crashed entirely. It's always possible that your settings file has become corrupt. Or perhaps these systems have between them gotten into some kind of strange feedback loop.
In the latter case particularlywhere the problem may indeed not reside in any one place at all, but rather arises out of the complex interaction of independent partsresolving the issue is going to present unusual difficulties. Diagnosis of simple defaults in ubiquitous systems will likely prove to be inordinately time-consuming by current standards, but systems that display emergent behavior may confound diagnosis entirely. Literally the only solution may be to power everything down and restart components one by one, in various combinations, until a workable and stable configuration is once again reached.
This will mean rebooting the car, or the kitchen, or your favorite sweater, maybe once and maybe several times, until every system that needs to do so has recognized the others and basic functionality has been restored to them all. And even then, of course, the interaction of their normal functioning may entrain the same breakdown. Especially when you consider how dependent on everyware we are likely to become, the prospect of having to cut through such a Gordian tangle of interconnected parts just to figure out which one has broken down is somewhat less than charming.