It's 10:40 p.m. on Sunday. Nothing has happened yet: no meetings, no conflicts, no difficult emails. And yet, your body is already exhausted by Monday.
How can something that hasn't happened make you tired?
The accountant living in your head
Before taking on any demanding task, the brain makes a silent calculation: how much energy will it cost me, and what do I get in return? Three areas are involved:
The anterior insula reads the body's state, like a car's dashboard. When it registers low reserves, it exaggerates the cost of what's coming.
The anterior cingulate cortex acts as the decision table. It places the projected cost against the reward and decides whether it's worth acting.
The lateral prefrontal cortex, the area responsible for decision-making and strategy, sustains your concentration while you work.
When that third area becomes depleted, the calculation gets distorted and the estimated cost of the next task rises. That's why a simple email, at six in the afternoon, can weigh as heavily as a complex problem at nine in the morning.
The clue they found in Paris
A team at the Paris Brain Institute (Wiehler and colleagues, Current Biology, 2022) looked for a physical trace of that depletion. They used magnetic resonance imaging to measure the chemistry of the lateral prefrontal cortex before and after a day of intense cognitive work.
The participants who worked for hours accumulated more glutamate (an excitatory neurotransmitter) in that area. With that accumulation, they tended to choose low-effort options and immediate rewards.
What can be said with some confidence today is that the brain regulates how much effort it accepts based on accumulated depletion.
Prospective fatigue works like a resource-management alarm and protects reserves before they run out.
How it shows up in the office
These studies were conducted in a laboratory. What follows is a reasonable projection onto the business world.
A leader with a high denominator may display four behaviours that at first glance read as character traits but have a chemical origin:
They postpone the strategic. Change seems enormous to them, and "that's how it's always been done" wins on energy savings.
They avoid difficult conversations. Listening well and reading the team's mood consumes resources that are scarce that day.
They put out fires and leave the vision for later. Solving the immediate costs less than sustaining a six-month plan.
Their patience runs short. The same area that curbs the emotional reaction operates with less margin.
In El impuesto invisible del liderazgo, I call this depletion the denominator of the Decisional ROI™: prospective fatigue divides the return of every decision. With a high denominator, the same intelligence yields less.
Three moves for tomorrow
These are practical, indicative rules, and their effect varies from person to person.
Move one heavy decision to the first block of the day. If the load builds up over the hours, the morning offers better ground. Relocating just one important decision already makes a difference.
Shrink the first step. "Redesign the commercial structure" triggers a huge cost estimate. "Write the list of current roles" lowers that cost and makes it easier to start.
Insert ten screen-free minutes between demanding meetings. They relieve the load accumulated during the day. Deep recovery happens during sleep, and breaks help as a complement.
Source: Alejandra Dabos. (October 30, 2026). Tu cerebro te cobra el cansancio por adelantado. Portal Psicología y Mente. https://psicologiaymente.com/psicologia/tu-cerebro-te-cobra-el-cansancio-por-adelantado