When people talk about fatigue, they reach for the language of energy: batteries draining, tanks running dry, people "running on empty." The metaphor feels intuitive, and it has shaped a generation of corporate responses such as resilience programmes, recharge days, sleep hygiene workshops. All well-intentioned and of them aimed at the wrong problem.
Fatigue, it turns out, is not primarily a readout of depleted fuel. Rather, it is a calculation, a signal the brain actively generates to tell you that the task you are doing may no longer be worth the effort. Change the cost benefit analysis and you can change the sense of fatigue.
The detail
The traditional view held that mental exhaustion reflects the depletion of some finite resource, the cognitive equivalent of glycogen in a marathon runner's legs. The difficulty is that researchers have struggled to find any such resource running out at the moment people report feeling exhausted. People who describe themselves as too drained to continue can perform at full capacity minutes later when the incentives change, finding hard to square with an empty tank.
What the evidence supports instead is that fatigue is the product of a cost–benefit analysis the brain runs continuously: is this task still worth the effort it is costing? Two studies show what happens to that analysis when effort is sustained. Blain, Hollard, and Pessiglione (2016) had people do a full day of demanding cognitive work and found their basic thinking was undiminished but their choices had changed. They became measurably more impulsive, favouring smaller, immediate rewards over larger, delayed ones. Massar, Csathó, and Van der Linden (2018) found the same pattern from a different angle: fatigued people systematically choose the easier option, even when the rewards on offer have not changed. In other words, fatigue does not drain capability first; it quietly re-prices effort, so the same task now feels more expensive and the same reward less worth pursuing.
Müller and Apps (2019) pulled these findings into a single framework that explains what the feeling of fatigue actually is: not a fuel gauge, but the output of the calculation itself. As the brain's estimate of a task's return on effort deteriorates, the sensation of tiredness rises. Agrawal, Mattar, Cohen, and Daw (2022) then answered the obvious question ‘why would the brain work this way?’ They propose that fatigue is a deliberate, adaptive design feature, not a malfunction. The brain generates tiredness to prise you away from work it has judged low-yield and push you toward more valuable alternatives, long before your physical energy reserves are anywhere near empty. Fatigue is your brain's chief financial officer flagging a poor return on invested attention.
Think about it this way. You’ve gone on a 15 mile run, and at mile 10 you are contemplating giving up. You are feeling tired and have had enough. Then someone promises you a large amount of cash to finish the run. Instead of stopping you find renewed energy to keep going, because the benefit of completing the run has changed significantly. Similarly, ploughing through the dreary drudge of administrative work after a while can result in the sense of having ‘had enough’, until you remind yourself of the purpose of getting the job done (such as taking the pressure off you whilst on holiday, or because doing the work means you can support your child through university). Reframing the reward turns the fatigue signals off and the motivation signals up.
Why this matters to business
Consider what your organisation actually runs on. In a multinational, the binding constraint is rarely capital or information; it is the sustained, high-quality judgement of a relatively small number of people making consequential decisions across time zones. The valuation account of fatigue has three direct implications for that constraint.
First, fatigue degrades decisions before it degrades performance. The Blain et al. (2016) finding is sobering precisely because the participants' basic cognitive performance held up; what shifted was their preference for immediate, easy rewards. Translated into what people do: the fatigued person does not visibly slow down. But at 9pm in the evening they may be more inclined to approve the convenient option, defer the hard conversation, and or accept the first workable answer. Nobody in the meeting notices anything wrong, least of all the leader but the personal cost benefit analysis in the brain is hard at work reframing the value of the effort. Second, fatigue is information about work design, not a character reading. If exhaustion is a signal that the brain has priced a task as low-reward relative to its effort, then a chronically fatigued team is telling you something diagnostic: the reward side of their ledger whether that be making progress, the meaning of the work they are doing, or the recognition they are receiving is not enough to maintain the effort. Treating that signal with a stress management course or advising the use of a mindfulness app is like giving painkillers to someone limping on a twisted ankle and sending them out for another run. The discomfort was never the main problem, it was a symptom pointing to an underlying issue.
Third, the signal is manipulable in both directions, which is an opportunity and a hazard. Because fatigue tracks perceived value rather than actual reserves, changing incentives, visibility of progress, or task variety genuinely changes how tired people feel and how well they choose. But the same logic explains why heroic cultures can push people far past sensible limits. Strong enough extrinsic pressure can override the signal for months. The notion of an energy tank metaphor at least implied a hard stop. The valuation account says there isn't one, until health breaks.
Why we need to think differently
Most corporate fatigue management is built on the depletion model, and it shows. We prescribe rest as the universal remedy, treat wellbeing as an individual responsibility, and locate the intervention outside working hours, as if the workday were a fixed withdrawal and recovery a private matter of deposits. The science suggests the leverage is inside the workday. Rest still matters, sleep in particular affects the same effort-valuation process. But if fatigue is a running commentary on the worthwhileness of work, then the design of the work itself is the primary intervention, and leaders, not employees, own it.
This also demands a different managerial response. When someone reports feeling burned out on a project, the depletion model asks, "How can we help you recharge?" The valuation model asks a better question: "What has made this work feel low-yield? And is that assessment correct?" Sometimes the brain's calculation is wrong, the payoff is real but invisible and the fix is to make progress and purpose clearer. Sometimes the calculation is right, the project genuinely is a poor use of that person's effort, and fatigue has diagnosed a portfolio problem faster than your strategy review did.
The steps leaders can take
The practical agenda follows directly from the mechanism: manage the perceived cost–benefit of effort, not just the hours worked. Protect your best judgement, not just your time. Schedule consequential, irreversible decisions early in the day and never at the end of long meeting blocks; the drift toward easy options is largest precisely when it is least visible.
Make returns on effort visible. Fatigue rises when reward signals go quiet. Shorten the distance between effort and evidence of impact. Reward smaller increments, close feedback loops, tell people specifically what their work changed.
Cut the cost side deliberately. Audit recurring meetings, approval chains, and reporting rituals annually for effort that produces no decision. Every unit of pointless effort raises the fatigue "price" of everything else.
Build variety into deep work. Because the signal pushes toward exploration, alternating task types, analysis, conversation, creation has the outcome of resetting the valuation in a way that grinding on a single task does not.
Treat fatigue reports as diagnostics. When a team says it is exhausted, investigate the work before prescribing recovery: What feels futile? Where has progress become invisible? The answers are usually actionable quite quickly.
Beware cultures that override the signal. High-pressure incentives can silence fatigue for a long time. If your top performers never report it, assume suppression, not superhuman stamina. The people who grasp what fatigue really means will stop treating fatigue as a maintenance issue and instead start seeing it for what it is: real-time market data on the value of the work their organisations ask people to do. Exhaustion, it turns out, is a very useful signal. Understood well, it is one of the sharpest management instruments you have.
References
Agrawal, M., Mattar, M. G., Cohen, J. D., & Daw, N. D. (2022). The temporal dynamics of opportunity costs: A normative account of cognitive fatigue and boredom. Psychological Review, 129(3), 564–585. https://doi.org/10.1037/rev0000309
Blain, B., Hollard, G., & Pessiglione, M. (2016). Neural mechanisms underlying the impact of daylong cognitive work on economic decisions. Proceedings of the National Academy of Sciences, 113(25), 6967–6972. https://doi.org/10.1073/pnas.1520527113
Massar, S. A. A., Csathó, Á., & Van der Linden, D. (2018). Quantifying the motivational effects of cognitive fatigue through effort-based decision making. Frontiers in Psychology, 9, Article 843. https://doi.org/10.3389/fpsyg.2018.00843
Müller, T., & Apps, M. A. J. (2019). Motivational fatigue: A neurocognitive framework for the impact of effortful exertion on subsequent motivation. Neuropsychologia, 123, 141–151. https://doi.org/10.1016/j.neuropsychologia.2018.04.030