"[S]ystems can function autonomously as long as their environment is completely specified & preferably constant" #readingToday
It follows directly from the definition of tractability that an intractable system also is underspecified. The consequences are both that the predictability is limited and that it is impossible precisely to prescribe what should be done. Underspecification is, of course, only an issue for the human and organisational parts of the system. For the technical parts, in so far as they work by themselves, complete specification is a necessity for their functioning. An engine or a machine can only function if there is a description of how every component works and how they fit together. It is in this sense that the performance of a technical system results from the parts. Technological systems can function autonomously as long as their environment is completely specified and preferably constant, in the sense that there is no unexpected variability. But this need of a complete technical specification creates a dilemma for socio-technical systems. For such systems the environment cannot be specified completely and it is certainly not constant. In order for the technology to keep working, humans (and organisations) must function as a buffer both between subsystems and between the system and its environment, as something that absorbs excessive variability when there is too much of it and provides variability when there is too little. The problem can in some cases be solved by decoupling parts of the system, or by decomposing it. But for an increasing number of systems this solution is not possible.
The ETTO Principle, Erik Hollnagel