A client told me last month she was taking Fridays off to recover from burnout. Six weeks in, she felt worse.
Her Fridays were quieter, but by Tuesday afternoon she was already depleted. The math didn't add up: 20% fewer hours, 100% of the exhaustion.
Here's what the research now confirms: Deloitte's 2025 Workforce Intelligence Report found that cognitive strain, not hours worked, is now the primary driver of burnout. Mental fatigue, decision friction, and constant context-switching have surpassed workload volume as burnout indicators for the first time.
This changes everything about how we think about sustainable work.
Over 20 years coaching 500+ leaders through professional transitions, I've watched the burnout conversation focus almost exclusively on hours. Work less. Take vacations. Set boundaries around time.
All good advice. All incomplete.
The executives I see aren't burning out from too many hours. They're burning out from too much cognitive friction packed into whatever hours they work.
In 2022, researchers at the Paris Brain Institute discovered something that finally explains why some days destroy you while others don't.
When you perform cognitively demanding work, a chemical called glutamate accumulates in your lateral prefrontal cortex. Under normal conditions, your brain has mechanisms to drain this buildup. But when cognitive demands are too high or too constant, glutamate accumulates faster than your brain can clear it.
The result: impaired decision-making, increased impulsivity, and preference for immediate rewards over better long-term choices.
Sound familiar? It's that moment when you know you should tackle the strategic project but find yourself answering emails instead. Your prefrontal cortex is literally compromised.
The study published in Current Biology measured this using magnetic resonance spectroscopy throughout an entire workday. Participants who did high-demand cognitive tasks showed significant glutamate accumulation. Those doing low-demand tasks did not.
Hours worked were identical. Cognitive impact was not.
This is biology, and it validates what most leaders feel but can't articulate: some work depletes you exponentially more than other work, regardless of time spent.
McKinsey research found that employees spend more than 60% of their working time navigating fragmented systems, unclear responsibilities, and high-friction workflows. Not doing their actual work. Managing the friction around their work.
The specific culprits from the research:
Context switching. Every time you shift between tasks, tools, or conversations, your brain pays a switching cost. Research indicates this can consume up to 40% of productive time and increase errors. That back-to-back calendar with five different projects across seven different apps? Each transition costs you.
Decision volume. CEOs make approximately 50 high-stakes decisions daily. But it's not just the big calls. Research on decision fatigue shows that trivial decisions deplete the same cognitive resources as consequential ones. Choosing what to address first in your inbox uses the same mental infrastructure as evaluating a strategic partnership.
Collaboration overload. McKinsey notes that senior executives often have calendars booked back-to-back in 15-minute increments. The irony: they need uninterrupted time to synthesize information and make good decisions. Instead, they get fragmented time and make worse ones.
Ambiguity processing. Unclear expectations, undefined scope, and decisions without sufficient information all require more cognitive effort than clear tasks. Your brain works harder when it's simultaneously doing the work and figuring out what the work is.
Fifty-six percent of executives report burnout, and the rate has climbed from 52% in 2023 to 56% in 2024. Some studies show 71% of CEOs experience burnout at least occasionally, with 32% reporting it frequently or near-daily.
Here's the pattern I notice in my work: leaders who track their hours find little correlation with their exhaustion levels. A 45-hour week of high-context-switching, ambiguous projects leaves them more depleted than a 55-hour week of focused, clear-scope work.
The math most people use: Hours worked = Energy spent.
The actual equation: (Hours worked) x (Cognitive friction per hour) = Energy spent.
Two hours of back-to-back meetings with unclear agendas and multiple stakeholders can cost more cognitive energy than six hours of focused project work. A day with 12 app switches, 47 Slack messages, and three "quick calls" depletes differently than a day with one deep work block, even if both are eight hours.
When my client took Fridays off, she was subtracting hours without changing the cognitive friction of Monday through Thursday. Same equation, same result.
The executives who maintain energy over years share a common approach: they manage cognitive load, not just time.
Audit friction, not hours. Track what depletes you for a week. Note the activities that leave you more tired than their duration would suggest. Context switches. Unclear meetings. Decisions without authority. Interruptions during deep work. This friction inventory reveals where the real cost is.
Batch by cognitive demand. Group similar types of thinking. A morning of three different strategic conversations costs more than three hours on one strategic topic. Your brain pays switching costs even between similar tasks. Batching reduces those costs.
Create decision boundaries. The research on decision fatigue is clear: trivial decisions deplete the same resources as important ones. Reduce the total number of decisions you make. Delegate. Automate. Create defaults. Every decision you eliminate preserves capacity for the ones that matter.
Protect synthesis time. McKinsey's research on executive effectiveness emphasizes that senior leaders need uninterrupted time to integrate information and apply judgment. This isn't optional. It's how good decisions get made. Block it. Defend it.
Notice the body signal. Glutamate accumulation doesn't just affect your thinking. It changes your behavior. When you start reaching for easy tasks, checking email compulsively, or feeling unable to focus, your brain is signaling that it's compromised. The signal is data. Honor it.
My client eventually realized that Fridays off was the wrong intervention. The four days she was working contained so much cognitive friction that no amount of recovery could offset them.
She started differently: mapping her week by cognitive load, not hours. The meeting that required her to switch between five different client contexts in 90 minutes. The project with undefined scope that required her to re-establish what "done" meant every time she touched it. The 23 Slack channels where she was mentioned but couldn't meaningfully contribute.
Over three months, she reduced cognitive friction by roughly 40% while keeping her hours almost the same. Her energy changed completely. The Fridays off became actual recovery rather than desperate catching-up.
The question isn't how many hours you can sustain. It's how much cognitive friction you can reduce in the hours you work.
Your body already knows which activities cost you more than they should. The tightness in your shoulders during certain meetings. The dread before specific types of work. The way some days leave you unable to think while others, just as long, leave you energized.
Those signals are legitimate data about cognitive load. The research now confirms what your nervous system has been trying to tell you: the hours are the container. What you put in them determines whether you can sustain the pace.
The world keeps accelerating. The Simplicity Protocol helps ambitious professionals do less to achieve more through weekly elimination strategies you can implement in 20 minutes or less.
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