You’ve probably heard it said that self-control – or what some people think of as willpower – is like a muscle. Use it too much and it gets fatigued, potentially to the point of exhaustion. The idea has become deeply embedded in pop psychology books, productivity blogs and even casual conversations. After a tough day of decision-making, we say we’re ‘mentally drained’, as if we’ve used up some internal energy or worn out our willpower muscle.
In psychology this idea is known as ego depletion in reference to the way that acts of self-control supposedly ‘deplete’ an inner store of mental energy. Skipped dessert at lunch? It’ll be harder to resist Netflix instead of working tonight. The model has an intuitive appeal. It’s tidy, metaphorical, and gives us an excuse to indulge when we feel worn out. Another part of its appeal may lie in the fact that it mirrors how willpower often feels from the inside, such as the heavy mental drag after a day of resisting temptation or making decisions, or the way distractions suddenly seem more alluring when you’re tired.
But what if it’s wrong? What if willpower doesn’t deplete at all?
The theory of ego depletion became wildly influential after its introduction in the mid- to late-1990s. Apparently backed by dozens of lab studies, it suggested that every act of self-control – resisting temptation, focusing attention, managing emotion – taps into the same limited internal resource (the same willpower muscle, if you like). Once that muscle is fatigued, we’re more prone to impulsivity, distraction and poor decisions.
The theory made its way into bestselling books, corporate training and even political life. The former US president Barack Obama once explained that he wore the same-coloured suits every day to save his decision-making power for the things that mattered. The idea wasn’t just popular – it seemed to be useful. It helped people explain their mental exhaustion and opened the door to strategies to help conserve willpower or build it up.
The more psychologists tried to pin down ego depletion, the more it slipped through our fingers
But over time, cracks began to show. In many of the experiments testing ego-depletion theory, participants would complete one task requiring self-control – such as ignoring distractions on a computer screen – and then attempt a second demanding task. According to the theory, their performance should drop on the second task. In everyday terms, this would be like spending the morning ignoring your phone to focus on work, only to find it harder to resist scrolling social media in the afternoon.
Yet meta-analyses that combined results across multiple studies failed to find consistent support for ego depletion. Several large-scale replication efforts, involving labs across the world, came back with mixed or null results. Even the most basic questions – what exactly is being depleted? – remained unanswered. Early versions of the theory linked depletion to blood glucose, but that explanation has been largely discredited. In short, the more psychologists tried to pin down ego depletion, the more it slipped through our fingers.
However, despite these challenges, supporters of the ego-depletion account still defended it, claiming that the tasks used in the studies weren’t difficult or long enough. For that reason, my colleagues and I set out to create a design that gave ego depletion multiple opportunities to manifest. We reasoned that if willpower really is like a muscle, then the longer someone engages in a mentally demanding task, the more fatigued or depleted they should become. Their performance on subsequent tasks – especially those that also require self-control – should get worse over time.
We ran a 35-minute online study that involved participants completing two alternating tasks. One, a challenging numerical version of the Stroop task – which required participants to quickly say how many digits appeared on screen, ignoring the numbers those digits represented – was designed to tax their cognitive control. The other, a global-local task was a bit like spotting the forest and the trees at the same time: sometimes you had to focus on the big picture, other times on tiny details, and quickly switch between the two. We used this second task to measure whether our participants’ ability to focus and respond effectively deteriorated as time went on.
In direct contradiction of the ego-depletion theory, as time wore on, our participants adapted, got faster, more accurate, and showed no systematic decline in performance, even after prolonged cognitive effort.
Crucially, we also varied the difficulty of the Stroop task: some participants received a ‘high-depletion’ version (with more frequent conflicting trials), while others did an easier version. If willpower really worked like a muscle, then our ‘high-depletion’ Stroop task was the mental equivalent of running uphill rather than on a flat – it should have drained participants’ reserves faster than the easier, flat-terrain version. But that’s not what we saw. Instead of slowing down, the participants in the ‘uphill’ condition kept pace, and in some cases even got quicker.
What looks like ‘depletion’ or fatigue might actually be a transition
If the ego-depletion model doesn’t fit how people’s self-control or willpower actually works, we need a new way to think about it. One promising alternative is metacontrol theory – a framework that makes a conceptual shift away from the idea of ‘mental resources’ to mental modes. First proposed by the cognitive psychologist Bernhard Hommel, this theory suggests that the brain operates along a continuum between two cognitive states: persistence and flexibility. You can think of it like a car with two gears: persistence is the low gear for steady climbing, flexibility is the high gear for cruising and taking in new routes.
In a persistent state or low gear, your brain narrows its focus. You’re more goal-driven, more resistant to distractions and more likely to power through a difficult task (of the kinds that we used in our study). In a flexible state or higher gear, you’re more open to alternative ideas, better at integrating new information and more likely to let go of rigid goals.
Neither mode is ‘better’. They’re context-dependent strategies. In daily life, you’ve probably felt this shift: pushing through the last part of a workout or study session in persistence mode, then relaxing into flexibility when chatting with friends or brainstorming ideas.
Persistence is great when you’re writing a paper or resisting a craving. Flexibility helps when you’re brainstorming or navigating unexpected challenges. And crucially, your brain naturally shifts between these states, especially when tasks are prolonged or rewards are uncertain.
From this perspective, what looks like ‘depletion’ or fatigue might actually be a transition. After an extended period of persistence, the brain may ease into flexibility – not because it’s run out of mental fuel, but because switching gears is adaptive. From an evolutionary perspective, our ancestors likely gained a survival advantage from readily switching between mental modes or gears rather than locking into one task until the point of exhaustion.
Not only does metacontrol theory better explain the way people’s performance changes over time, it also aligns with current neurobiology (unlike ego-depletion theory). It links changes in cognitive mode to dopaminergic activity in different brain circuits – specifically, the prefrontal cortex and the basal ganglia. These systems are known to regulate the balance between focused persistence and flexible adaptation. In simple terms, brain chemistry can nudge us toward different modes of thinking. For example, when dopamine levels rise in certain areas at the front of the brain, we tend to become more persistent and focused on a single goal. When dopamine shifts to deeper brain areas, it helps us become more flexible and open to new ideas.
All of this has practical implications for how we think about effort, self-discipline and failure in everyday life. From a first-person perspective, the phenomenology of a ‘lapse’ – mind-wandering, craving a break, or suddenly rethinking your goals – may actually reflect this adaptive gear-shifting, not a failure of character or a depleted willpower muscle.
Improving willpower may require less emphasis on grit – and more on insight
If willpower isn’t something we lose over time, but a mode we shift out of, then moments of distraction or fatigue may not reflect weakness – they may reflect natural transitions in the cognitive system. And those transitions can be shaped by context, motivation, environment and feedback.
Sometimes, a short break isn’t failure. It’s recalibration.
In other words, when you experience mental fatigue or what feels like weakening willpower, it is not necessarily a sign that you need to push harder. Sometimes, what we interpret as depletion might actually be the system doing exactly what it’s evolved to do. In these situations, it might be wiser to pause, reset or switch strategies. In practical terms, this might mean stepping away from your desk after struggling with a tricky report to take a short walk, or switching from writing an essay to organising your workspace. By changing the type of mental demand, you give your brain a chance to reconfigure its control mode without ‘burning out’.
If it’s time to retire the ‘willpower as muscle’ metaphor, then what could be an alternative? I propose imagining your willpower as a car with two gears – not something that gets worn out, but something that changes gears based on your environment, your goals and your internal feedback – the brain’s ongoing monitoring of how well your current strategy is working, based on signals like perceived effort, progress toward the goal and the rewards you expect to get.
This doesn’t mean we should abandon discipline, but that improving willpower may require less emphasis on grit – and more on insight (that is, better understanding the way your brain monitors, modulates and adapts). For this we need more nuanced psychological models of willpower – ones that reflect how the brain actually works, rather than how we wish it did.
