Why are socio-technical systems non-deterministic?

Why are socio-technical systems non-deterministic?
Ans: Socio-technical systems are non-deterministic partly because they include people and partly because changes to the hardware, software, and data in these systems are so frequent. The interactions between these changes are complex and so the behavior of the system is unpredictable. This is not a problem in itself but, from a dependability perspective, it can make it difficult to decide whether or not a system failure has occurred, and to estimate the frequency of system failures. For example, say a system is presented with a set of 20 test inputs. It processes these inputs and the results are recorded. At some later time, the same 20 test inputs are processed and the results compared to the previous stored results. Five of them are different. Does this mean that there have been five failures? Or are the differences simply reasonable variations in the system’s behavior? You can only find this out by looking at the results in more depth and making judgments about the way the system has handled each input.