Please Do Not Disturb
When a control system is humming along, the gap between the desired and current states is so small that the frequency of command issuance by the Decision Maker component is essentially zero; all is well and goal attainment is on track. However, with the universe being as messy as it is, unseen and unpredictable “disturbances” can, and do, enter the system at any point of access to the structure.
If the sensors and/or actuators can’t filter out the disturbances or are malfunctioning themselves, then true control of the production system may be lost. Perceptions and commands get distorted and the distance between goal attainment and “reality” will be perceived as shorter or longer than they are. D’oh! I hate when that happens.