Their roles should not be defined by default or assumed, but must be evaluated and assessed. Humans vary in performance under workload and in response to their environment. Humans can be seen as threats and vulnerabilities, but they also act as counter-measures. Operators can make or break a system. They can find ways around using a system or obviate large chunks of capability.
Training needs to be part of the system.
On a project Systems Engineers must have and use soft skills to sell the Systems Engineering process and product. The case for Systems Engineering on a project is not always clear to all concerned, especially when time and resources are tight. The process and products of the project's Systems Engineering effort must be marketed at all levels of management. Understanding customers' strategic values and objectives and how this leads to increased motivation in a positive feedback cycle is beneficial to all concerned. Customer expectation needs to be managed.