Demand and performance do not move together indefinitely. There is a region where more demand improves output and a region where it does not, and the transition between them is the practically important part.
The relationship is a curve, not a line
Performance under increasing demand tends to rise, level off and then fall, which is why both boredom and overload produce poor work for different reasons.
The peak sits at different points for different tasks, and it is lower for complex work requiring judgement than for familiar work requiring speed.
Which means the same demand can be productive for a routine task and clearly excessive for one requiring careful thought, in the same person on the same day.
The two states feel different
Pressure typically presents as focus, urgency and a narrowing onto the task, and time passes without much notice.
Overload presents as difficulty holding the thread, rereading, switching between tasks without completing any, and a rising sense that everything is equally urgent.
The switching is the most reliable indicator, because it reflects a working memory that can no longer hold the current task steady against competing demands.
Recovery separates them more clearly than intensity
Pressure is compatible with recovery, so an intense period followed by a lighter one leaves capacity restored and no residue in the following week.
Overload is characterised by the absence of that return, where the intense period ends and the fatigue does not lift on the normal timescale.
Which is why sustained moderate demand without recovery frequently causes more harm than short periods of very high demand with recovery built in.
Duration changes the reading
A demanding week is a different exposure from a demanding year, even if the daily experience is similar.
Short intense episodes are generally well tolerated, and people often describe them positively afterwards, particularly where the effort produced something.
Prolonged demand without an endpoint removes that framing, since there is no completion to anticipate and no point at which the level is expected to drop.
Why the distinction is practically useful
Advice aimed at pressure, such as prioritising and working in focused blocks, applies well below the peak and poorly above it.
Above the peak the useful moves are subtraction and renegotiation, since better technique applied to an excessive volume mostly increases the volume that can be attempted.
Where overload has become sustained and recovery is not returning, that is the pattern occupational health describes as burnout, and it is a matter for a clinician rather than for time management.