The leader who cannot adapt. The negotiator who will not bend. The coach who repeats the same failing strategy. We call it stubbornness, inflexibility or poor judgement. A growing body of research suggests another possibility: in some cases, these may be cognitive consequences of insufficient sleep — a condition that can reduce the brain’s capacity for flexible thinking while leaving people less aware of their own impairment.
He was the most experienced negotiator on the team. That was why he was leading the deal. But three weeks into the process, his colleagues noticed a change. The creative options that had characterised his early proposals disappeared. His positions hardened. Counteroffers were dismissed rather than explored. When the other side presented a novel structure, he rejected it within minutes — not because he had analysed it, but because it did not fit the framework he had already committed to.
His team attributed it to stress. Stress was almost certainly part of the picture. But his sleep history suggested that cognitive rigidity had become part of the problem. He had been sleeping fewer than five hours a night for eleven consecutive days while managing the deal across three time zones. The rigidity was not necessarily a deliberate strategy. It may have been a symptom of accumulated sleep loss.
What sleep deprivation does to flexible thinking
A 2025 scoping review in Frontiers in Neuroscience examined the effects of sleep deprivation on cognitive flexibility across multiple studies and experimental paradigms.
The overall pattern pointed towards impairment, although the findings were not uniform. Eight studies reported reduced cognitive flexibility, six found no significant decline, and two observed temporary improvements under particular conditions. A further study found different outcomes according to participants’ weight status, illustrating how individual characteristics may influence the cognitive effects of sleep restriction.
A cautious interpretation is therefore not that insufficient sleep always creates rigid thinking, but that sleep loss can increase the risk of it.
Sleep deprivation does not appear to affect every cognitive function equally. Familiar and highly practised tasks may sometimes remain relatively stable, particularly over short periods. A person may still follow procedures, execute familiar sequences and maintain performance on routine skills.
More demanding executive functions — including attentional control, inhibition, strategy switching and adaptation to changing information — may become increasingly vulnerable.
These are precisely the capacities that leadership under real conditions requires: generating alternatives, evaluating novel information on its merits and revising a position when new evidence appears.
There is also a useful conceptual parallel with decision fatigue. Both conditions may encourage greater reliance on familiar responses, habitual rules and simplified choices under sustained cognitive demand.
Sleep loss and accumulated decision load are not identical phenomena, and their mechanisms should not be treated as interchangeable. But when they occur together, they may increase the likelihood of attentional lapses, weaker inhibition and rigid judgement in demanding environments.
A leader who is both sleep-deprived and decision-fatigued may therefore be operating with a compounded deficit in precisely the cognitive capacities their role demands.
The invisibility problem
A 2026 randomised crossover study involving international-level male karate athletes, published in Medicine, found that restricting sleep to four hours impaired reaction time, inhibitory control measured through the Stroop task, and several measures of physical performance compared with an eight-hour sleep condition.
The athletes were elite. Their training and experience did not protect them from the cognitive consequences of insufficient sleep.
The study did not directly measure cognitive flexibility, but it connects to a broader pattern established by Hans Van Dongen, David Dinges and colleagues more than two decades ago: people who are chronically sleep-restricted may underestimate the degree to which their objective performance has deteriorated.
This is the feature that makes sleep-related cognitive rigidity so dangerous in professional contexts.
The person does not feel rigid. They feel certain.
When cognitive flexibility narrows, fewer alternatives are generated. When fewer alternatives reach conscious consideration, the remaining option can feel more obviously correct.
Rigidity begins to resemble conviction.
The leader who cannot adapt may experience themselves as someone who simply knows what they want. The negotiator who dismisses alternatives may feel decisive rather than impaired. The coach who repeats the same strategy may interpret persistence as consistency.
The difference between conviction based on clear thinking and conviction reinforced by cognitive impairment can be difficult to see from the inside.
In my coaching practice, I have learned to treat sudden inflexibility as a diagnostic signal rather than immediately interpreting it as a personality flaw.
When a client who is normally creative becomes rigid, when a leader who typically considers multiple perspectives begins dismissing alternatives, or when a negotiator skilled at finding mutual gain becomes positional, the first question is not always about strategy.
It may be about sleep.
The circadian dimension
Christian Cajochen and Christina Schmidt’s 2025 review in the Annual Review of Psychology added an important circadian dimension to the relationship between sleep and cognitive performance.
The strength of circadian effects depends on accumulated sleep debt and on the cognitive domain being tested. Flexible thinking, which relies heavily on executive control and prefrontal resources, may be particularly sensitive to the interaction between insufficient sleep, time awake and circadian phase.
The practical implication is that the timing of cognitively demanding work matters independently of total sleep duration.
A person may have slept for what appears to be an adequate number of hours and still be working during a period of reduced circadian alertness. At such times, attentional control, inhibition and adaptive thinking may be less reliable.
There is no universal hour at which everyone becomes cognitively inflexible. Chronotype, sleep quality, prior sleep debt, time awake, work schedule and individual biology all matter.
The interaction between sleep quantity, sleep quality and circadian timing creates a shifting cognitive environment that most professionals navigate without fully recognising that it exists.
What a mental performance coach does with this
The coaching interventions follow from the science.
Track sleep before attributing rigidity to personality or strategy
When a client’s thinking narrows, ask about sleep before concluding that the problem is character, motivation or competence.
How many hours have they slept?
For how many consecutive nights?
Has their sleep schedule changed?
Are they working across time zones?
Are they waking repeatedly?
Are they relying on stimulants to extend the working day?
The physical foundations of mental capacity should be among the first variables examined, not the last.
Protect flexible-thinking windows
Schedule work that requires cognitive flexibility — strategy sessions, creative problem-solving, negotiations and difficult conversations — during periods when the client’s sleep history and circadian rhythm are most likely to support executive function.
This should be tailored to the client’s individual sleep patterns, chronotype and periods of highest alertness rather than following a universal timetable.
Routine administration and complex decision-making do not place the same demands on the brain. They should not automatically be scheduled in the same way.
Use inflexibility as a coaching signal
Teach clients to recognise their own rigidity as information rather than identity.
“I notice that I am dismissing alternatives without evaluating them.”
“I keep returning to the same solution.”
“I feel unusually certain, but I cannot explain what evidence changed.”
These are metacognitive observations that can function as an early warning system.
The observation does not eliminate the impairment. It creates a pause in which the person can choose to defer rather than decide.
Design for the impaired state, not only the optimal state
Professionals often design their schedules, decision processes and commitments as though they will always be operating at their cognitive best.
They will not.
There will be disrupted nights, travel, illness, family pressure, emotional strain and periods of accumulated workload.
A coach who helps a client build systems that function adequately when cognitive flexibility is reduced is building resilience into the architecture.
Those systems may include pre-committed decision criteria, trusted advisers empowered to challenge assumptions, mandatory pauses before consequential choices and second reviews of decisions made after severe sleep restriction.
The aim is not to depend on perfect cognitive performance.
It is to prevent temporary impairment from becoming a permanent consequence.
The negotiator I described recovered the deal, but not through improved negotiation technique.
He began by sleeping.
After two nights of adequate sleep, his colleagues noticed a clear change in the way he approached the discussion. The creative options began to return. His positions became less defensive. Structures he had dismissed days earlier were reconsidered.
The rigidity softened.
This does not prove that sleep was the only cause. Stress, pressure, ego and strategic commitment may all have contributed.
But restoring sleep changed the conditions under which he was thinking.
He was not a different person.
He was the same person operating with a better-maintained brain.
Sleep is not passive rest from performance. It is part of the biological maintenance that makes flexible performance possible.
Before treating rigid thinking as a permanent character flaw, it is worth asking a simpler question:
How much sleep has this brain been trying to function without?
ALTIUS Note
This article belongs to the ALTIUS editorial library: evidence-based essays on Human Performance, Leadership and Society.
Tags: Human Performance · Health · Leadership
Selected Research Foundations
Sun, X., Qu, Z., Zhang, X., Zhang, Y., Zhang, X., Zhao, H., & Zhang, H. “The Effects of Sleep Deprivation on Cognitive Flexibility: A Scoping Review of Outcomes and Biological Mechanisms.” Frontiers in Neuroscience, 19, 1626309 (2025). DOI: 10.3389/fnins.2025.1626309.
Amri, A., Faleh, J., Ben Aissa, M., et al. “Effects of Sleep Restriction on Cognitive and Physical Performance in Elite Karate Athletes: A Randomized Crossover Study.” Medicine, 105(11), e48064 (2026). DOI: 10.1097/MD.0000000000048064.
Cajochen, C., & Schmidt, C. “The Circadian Brain and Cognition.” Annual Review of Psychology, 76, 115–141 (2025). DOI: 10.1146/annurev-psych-022824-043825.
Van Dongen, H. P. A., Maislin, G., Mullington, J. M., & Dinges, D. F. “The Cumulative Cost of Additional Wakefulness: Dose-Response Effects on Neurobehavioral Functions and Sleep Physiology from Chronic Sleep Restriction and Total Sleep Deprivation.” Sleep, 26(2), 117–126 (2003). DOI: 10.1093/sleep/26.2.117.
