People generally assume that large events cause most of their stress. The pattern in everyday life runs differently, because small recurring demands have properties that major events do not.
Recovery requires an interval that repetition removes
A single demanding episode is followed by a return towards baseline, and that return is what prevents the physiological changes involved from persisting.
Minor stressors recur before the return is complete, so each new instance begins from a slightly elevated starting point rather than from rest.
Over a week this produces a raised baseline that never resolves, which is a different physiological situation from one intense episode followed by three quiet days.
Small stressors are not treated as legitimate
A bereavement or a redundancy is recognised by other people, attracts sympathy, and frequently justifies adjustments to workload or expectations.
A slow computer, an unpredictable commute or a colleague who interrupts constantly attracts none of that, because each instance is genuinely trivial.
The absence of recognition means nothing is done about them, and doing nothing is precisely what allows the accumulation to continue.
Unpredictability multiplies the cost
A demand that arrives at a known time can be prepared for, and preparation reduces the response it produces.
Irritations that occur at unpredictable intervals cannot be prepared for, so they maintain a state of low-level readiness between occurrences.
That readiness has a cost of its own, which is why a job with unpredictable interruptions can be more tiring than one with a heavier but scheduled workload.
Attribution goes to the wrong place
Because no individual instance seems capable of causing the fatigue somebody feels, the fatigue gets explained by something else entirely.
People commonly conclude that they are not coping well, or that something is wrong with them, rather than that a large number of small demands is sufficient explanation.
That conclusion tends to add a further layer of strain, since it converts an environmental problem into a judgement about the self.
Removing a few sources works better than tolerating all of them
Because the effect is cumulative, eliminating even a small proportion of recurring irritations changes the total in a way that is disproportionate to how minor each one seems.
The candidates worth removing are the ones that recur most often rather than the ones that feel worst, since frequency drives the accumulation.
Where strain has persisted for months and is affecting sleep, mood or physical health, that is a reason to speak to a doctor rather than to continue adjusting the environment alone.