Psychology › Emotion, motivation & happiness › Self-control and willpower
Ego depletion ('willpower is a muscle')
1998; failed 2016· Finding or experiment
Weak or failed to replicateFamous but not holding up in careful repeats.
The theory that self-control draws on a limited resource that gets used up, like a tiring muscle.
See it on the Psychology map →What it says
In 1998 Roy Baumeister and colleagues seated hungry students before fresh chocolate-chip cookies; some could eat them, others had to eat radishes instead. Radish-eaters then gave up on unsolvable puzzles after about 8 minutes, versus about 20 for the others. Hundreds of studies seemed to confirm that resisting one temptation weakens the next. A 2007 study claimed sugary drinks restored willpower. The idea spread through the 2011 bestseller Willpower and popular talk of 'decision fatigue'.
Why it matters
It shaped self-help and management advice for a decade. Its failure shows that a plausible idea, repeated in hundreds of small studies, can still be wrong.
The evidence
Status: weak or failed to replicate. A 2016 test across 23 labs with over 2,000 people found an effect near zero, and a 2021 test of over 3,500 people, co-designed by proponents, found a tiny one.
Open questions
Whether related claims hold, such as 'decision fatigue' in Israeli parole judges, whose apparent pre-lunch harshness may reflect how cases were scheduled.
Connections (2)
▸The replication crisis overturned Ego depletion ('willpower is a muscle')Well replicated
The connection
A 2010 meta-analysis of 198 experiments reported a solid effect, but a 2014 reanalysis correcting for unpublished null results suggested it might be near zero. Direct tests followed: a 2016 registered replication across 23 labs and 2,141 people found almost nothing, and a 2021 effort in 36 labs, involving the theory's proponents, found an effect too small to matter.
Who showed it and when
Evan Carter and Michael McCullough's reanalysis, 2014; Martin Hagger and Nikos Chatzisarantis's multi-lab project, 2016; the 2021 test led by Kathleen Vohs, a longtime Baumeister collaborator.
The evidence
Preregistration fixes methods and analyses in advance, so results cannot be massaged afterward; both large tests were preregistered.
Open questions
Baumeister argued the lab tasks were too mild to drain willpower; critics reply that an effect invisible in 36 labs explains little about daily life.
▸Ego depletion ('willpower is a muscle') claimed limited fuel for Self-control and willpowerWeak or failed to replicate
The connection
Baumeister's 'strength model' said self-control runs on one limited resource: resisting cookies or suppressing emotions uses it up, leaving less for the next task, like a tired muscle. A 2007 study claimed glucose restored it, and popular advice urged a snack before hard decisions. But the brain's sugar use barely changes with mental effort, and the effects failed to replicate.
Who showed it and when
Roy Baumeister, Ellen Bratslavsky, Mark Muraven and Dianne Tice at Case Western Reserve University, 1998; Matthew Gailliot's glucose studies, 2007; Baumeister and John Tierney's Willpower, 2011.
How solid is it?
Hundreds of small early studies supported it, but large preregistered tests in 2016 and 2021 found effects near zero, and the glucose claim was criticized on physiological grounds.
Open questions
Mental fatigue feels real; whether it reflects shifting priorities and attention, as Michael Inzlicht's process model argues, rather than a drained resource is debated.