There’s a certain kind of person you’ll recognise in organisations under pressure. It may or may not be you.
They’re often there first and last to leave, they’ve stopped taking decent breaks, and they’re running on adrenaline, coffee, energy drinks and the occasional sugary snack. And if you suggest they pull back or ease off, they’ll tell you with complete conviction, that they’re fine. Or better than fine, even.
They aren’t being dishonest. They think they are.
Drew Dawson and Kathryn Reid published a sweet little study in Nature (a top-shelf journal) back in 1997. They took the performance decline that’s clear in prolonged wakefulness and quantified it in a unit we’re familiar with. Blood alcohol.
Blood alcohol levels
They found that after 17 to 19 hours without sleep, performance on cognitive and motor tasks drops to a level equivalent to a Blood Alcohol Concentration of 0.05%.
That may not sound much, so here’s some context.
In Aotearoa New Zealand, and ignoring the under 20-year-olds where the limit is zero, the limit is 250mcg of alcohol per litre of breath or 50mg of alcohol per 100ml of blood. 50mg of alcohol per 100ml of blood is a 0.05% reading. That’s the adult drink-driving limit. Or, in the words of the NZ Transport Agency, ‘You can’t drive if you have more than 250 micrograms of alcohol per litre of breath, or more than 50 milligrams of alcohol per 100 millilitres of blood’ (emphasis added).
Naturally, the longer you’re awake, the worse your performance gets.
If you’ll excuse the pun, that’s sobering.
Someone working a long day, who may have been up early and is shorter on sleep is, on the evidence we have, working at a level that we have collectively decided is too impaired to be in charge of a car. By law. We’d take their keys off them, call an Uber, and put them to bed.
But not if they’re at work.
Instead, we might be asking for complex problem solving, decision making, information synthesis, people management, and so on.
Fatigue equals impairment
Williamson and Feyer ran a similar study in 2000 with the same results. Fatigue equals impairment, which is no surprise to safety-critical jobs like pilots, healthcare workers, long-haul drivers, let alone policy makers and, the poor things, parents with babies and young children.
Later work accurately questioned the very high end of the relationship, showing that no amount of wakefulness really matches serious intoxication. But at the lower end we’re talking about, the 17ish hours awake being equivalent to 0.05% BAC is solid? That’s solid.
Here’s the thing. I don’t imagine this comes as a significant surprise. You’ve probably experienced it. But that’s not where I’m going.
The part that niggles more is how genuinely poor we are at self-assessment. Self-report is, generally, notoriously unreliable across a range of domains, but in this area, has a fishhook. Sleep loss seems to breed overconfidence.
We’re genuinely bad at self-assessment
In studies of sustained wakefulness, people grew more certain their judgments were right as they got more tired, and overconfidence appear strongest exactly when they were wrong (Alhola & Polo-Kantola, 2007). Some people do recognise, and we all have different levels of stamina and need for sleep, so I’m not saying it’s a perfect finding, but when the failure is obvious, it trends the same way. We inflate our self-assessment. A tired brain scoring its own performance tends to rate high, not low.
So the sense, or even the unshakeable conviction, we have, that we’re fine, is being generated from the same system doing the impaired work. To frame it in the work of Dawson and Reid, it’s like asking a person after their sixth drink how drunk they are and expecting them to give you a correct assessment. But we wouldn’t treat their confidence as reassurance about driving.
Consequently, the “I’m fine” isn’t someone being dishonest, but inaccurate. We simply can’t have full trust they right, especially the longer they’ve been at it and the more confident they feel. Equally, we’re not blaming them.
Ok, so what?
A non-exhaustive list
First, watch outputs rather than how they present. Fatigue shows up in the quality of the work: poorer decisions, fewer options considered, alternative views more quickly dismissed, responses that aren’t updated as situations change, missed risks, dropped details, and emotional regulation suffers, let alone how interpersonal interactions change.
Second, we already know that responsibility can’t sit with them. It must sit with those around them, including the structures and processes the organisation has in place. It could be mandated shift length and rotations, a culture where being stood down is considered normal operational protocol not an insult or evidence of weakness, norms where colleagues can call it (including junior colleagues), protocols where, for example, the Health and Safety officer can instruct you to go home, regardless of seniority or power differential, and so on. Obviously, there are more, and they will be tailored to your context.
Third, none of this is soft. These are not wellbeing issues to be filed away for a later workshop on personal management. This is about manging human performance as organisations manage any critical asset thew degrades under load: with maintenance, monitoring, and due care. Fatigue is the same kind of risk. It just happens to sit inside people’s skulls.
Their resistance is not a sign they’re coping. On evidence, it’s one of the more reliable signs they aren’t.
Photo credit: Photo by Sujin c on Unsplash
References
Agyapong-Opoku, F., Agyapong-Opoku, N., & Agyapong, B. (2025). Examining the effects of sleep deprivation on decision-making: A scoping review. Behavioral Sciences, 15(6), 823. https://doi.org/10.3390/bs15060823 [Recent review confirming impaired decision-making under sleep loss, strongest for complex decisions under uncertainty.]Dawson, D., & Reid, K. (1997). Fatigue, alcohol and performance impairment. Nature, 388(6639), 235. https://doi.org/10.1038/40775
Alhola, P., & Polo-Kantola, P. (2007). Sleep deprivation: Impact on cognitive performance. Neuropsychiatric Disease and Treatment, 3(5), 553-567. [Reviews the overconfidence-under-sleep-loss finding, and notes that self-assessment accuracy is variable.]
Dawson, D., & Reid, K. (1997). Fatigue, alcohol and performance impairment. Nature, 388(6639), 235. https://doi.org/10.1038/40775
Dawson, D., Sprajcer, M., & Thomas, M. (2021). How much sleep do you need? A comprehensive review of fatigue related impairment and the capacity to work or drive safely. Accident Analysis & Prevention, 151, 105955. https://doi.org/10.1016/j.aap.2020.105955
Williamson, A. M., & Feyer, A. M. (2000). Moderate sleep deprivation produces impairments in cognitive and motor performance equivalent to legally prescribed levels of alcohol intoxication. Occupational and Environmental Medicine, 57(10), 649-655. https://doi.org/10.1136/oem.57.10.649