Ego depletion is the finding that exerting self-control on one task measurably reduces a person's capacity for self-control on a later, unrelated task — willpower behaves less like a fixed trait and more like a muscle that tires with use. This matters far beyond diet and exercise: any decision requiring active self-regulation, including professional judgment calls, draws on the same limited resource.
The unsettling implication is that decisions we assume are made purely on the merits — a judge's ruling, a doctor's diagnosis, a hiring manager's evaluation — can be measurably swayed by something as mundane as how long it's been since the decision-maker's last break. This isn't a claim that professionals are lazy or biased in the usual sense; it's a claim that mental energy is a real, finite input to judgment, on par with the facts of the case itself.