In discussing what makes a job the "least stressful"...

... consider that, in this context, the opposite of stress is control.

Is that true? For some, I would think, too much control would lead to stress. Let's say much was expected of you. You were supposed to be brilliant, high-achieving, and productive. But it was your responsibility to define your tasks, to figure out how to accomplish them, to set your own standards about what constitutes excellence, and to put time — any time, whenever you want, night or day, weekdays or weekends — into doing what you've decided is appropriate to do.

There is some reason to think that people feel best when they are in the psychological state called "flow," which is defined as having 8 components:

First, the experience usually occurs when we confront tasks we have a chance of completing. Second, we must be able to concentrate on what we are doing. Third and fourth, the concentration is usually possible because the task undertaken has clear goals and immediate feedback. Fifth, one acts with a deep but effortless involvement that removes from awareness the worries and frustrations of everyday life. Sixth, enjoyable experiences allow people to exercise a sense of control over their actions. Seventh, concern for the self disappears, yet paradoxically the sense of self emerges stronger after the flow experience is over. Finally, the sense of the duration of time is altered; hours pass by in minutes, and minutes can stretch out to seem like hours. The combination of all these elements causes a sense of deep enjoyment that is so rewarding people feel that expending a great deal of energy is worthwhile simply to be able to feel it.

Can you get there within the "least stressful" job, university professor? Of course. But you'd better be good at defining realistic tasks that will look accomplished when they are accomplished. You'd better be able to get into the zone where you feel a sense of effortless expertise.

Mihaly Csikszentmihaly's book "Flow" identifies surgery and rock climbing as 2 activities that produce flow for the people who have the appropriate expertise. There, the tasks are specific, and the feedback about whether you are doing them right is clear. Compare a scholarly book project, which might take years, where you might wonder whether what you are writing is too dull or too controversial or unsupported by the data you're trying to use or who knows what your colleagues — your rivals? — will say about it at some unknown point in the future if you ever get this damned thing done?