HabitsPersonal Growth

Willpower

Roy Baumeister and John Tierney

Baumeister's research established that self-control draws on a limited resource that depletes with use across a day. That is the empirical case behind Book 3's Chapter 4 claim: a plan that runs on willpower degrades every week, while a plan built on environmental design holds steady when you're tired. His prescriptions — precommitment, fewer daily decisions — are the direct ancestor of 'design defaults, not exceptions.'