Lack of control or choice. The unpredictable nature of one's work, for example. And, when activities must be speeded up due to deadlines, when extra work is added unexpectantly, or when a person must work near maximum capacity for long periods. And, more stress is felt in situations over which one has little control. Chronic stress at work can cause burnout .
Threat has to do with one's idea of control.
One's personal sense of control in any situation comes from believing one can reach desired goals. It is threatening for a person to feel that he or she lacks competence to cope with a particular demand. A perceived lack of control is as important as actual lack of control in causing us to feel threatened. An inability to control stressors is very similar to the conditions that cause learned helplessness. One of many causes of stress.