Two jobs with identical hours and identical volumes of work can produce very different levels of strain. The variable that separates them most consistently is how much say the worker has over how the work gets done.
Demand and discretion are separate dimensions
Occupational health research has long treated the psychological demands of a job and the worker's decision latitude as two independent axes rather than one.
High demand combined with high discretion describes work that is busy and often absorbing, and it is not associated with the same harms as high demand alone.
High demand combined with low discretion is the combination repeatedly linked with poorer health outcomes, and it describes a great many frontline and process-driven roles.
Predictability does similar work
Control includes knowing what is coming, since a person who can anticipate a demand can prepare for it and pace themselves through it.
Unpredictable scheduling removes that even when total hours are modest, because the worker must remain available for periods they are not being paid for.
The strain is generated by the standby state itself rather than by the work performed, which is why irregular part-time schedules can be harder than steady full-time ones.
The physiological account is straightforward
The stress response is well suited to short bouts followed by resolution, and its cost comes from being sustained rather than from being triggered.
Having a means of acting on a demand allows the response to complete, because effort leads to resolution and the system returns toward baseline.
Where nothing can be done, the demand remains and the response is maintained, which is the mechanism behind the observation that helplessness is more damaging than effort.
Small discretion produces disproportionate effects
Studies of workplace interventions repeatedly find that quite limited increases in control, such as input into rota order or the sequence of tasks, register clearly on strain measures.
The size of the change matters less than its existence, since even a narrow choice converts the worker from a recipient of instructions into a participant.
Which is why consultation that turns out to be decorative tends to make matters worse, as it removes the belief in control without removing the demand.
What this changes about advice
Individual stress management addresses the response, and it does so usefully, but it leaves the demand-control ratio exactly where it was.
Identifying which specific decisions a person cannot make is often more productive than measuring how much work there is, because the former can sometimes be negotiated.
Where neither the demand nor the discretion can move, the honest reading is that the job is the source, and treating that as a personal coping failure is both inaccurate and unhelpful.