Definition
The Yerkes-Dodson law is the classical psychology finding that performance rises with physiological arousal up to an optimum, then falls as arousal continues to increase. The relationship traces an inverted-U curve: too little arousal underperforms, too much underperforms, and there is a peak between them.
The law was published in 1908 by Robert Yerkes and John Dillingham Dodson based on experiments with mice and electric stimuli. It has held up — with refinements — as one of the most replicated relationships in performance psychology.
Why it matters
How it works
Arousal is the physiological readiness state — heart rate, attention focus, cortisol, alertness — that the body brings to a task. The Yerkes-Dodson curve says performance follows an inverted U as arousal increases. At very low arousal you are sleepy and inattentive; at very high arousal you are anxious and rigid; somewhere in between is the level where attention is sharp and movement is fluid.
The refinement the original paper added is that the peak shifts with task difficulty. Complex cognitive tasks (writing, analysis, learning) peak at lower arousal — too much stress hampers reasoning. Simple physical tasks (sprinting, lifting) peak at higher arousal — adrenaline helps. Match the arousal to the task: low-stakes morning for the deep work, higher-stakes deadline for the simple execution.
Clear uses Yerkes-Dodson implicitly when he introduces the Goldilocks rule. The just-manageable difficulty level the rule prescribes is the arousal-management equivalent: enough challenge to engage, not so much to overwhelm. Habit design that keeps practice in the upper portion of the curve sustains motivation without burning out the practitioner. Habits that habitually push past the peak — chronic high stress, perpetual deadline pressure — degrade performance and shorten careers.