Charles Duhigg opens The Power of Habit by introducing the neurological structure underlying all habits: a three-part loop consisting of a cue (a trigger that initiates the behavior), a routine (the behavior itself), and a reward (the benefit that reinforces the loop, making it more likely to recur).

How Duhigg establishes this framework:

• Drawing on neuroscience research, he explains that habits form in the basal ganglia, a brain region associated with automatic, non-conscious behavior — meaning well-established habits genuinely operate outside of active, deliberate decision-making
• This automaticity is what makes habits both powerful (freeing cognitive resources for other tasks) and difficult to change (since they bypass the conscious decision-making process that could otherwise interrupt them)
• Duhigg illustrates this loop through concrete case studies, showing how understanding this specific three-part structure — rather than treating habits as simply "willpower" or "discipline" — provides genuine leverage for behavior change

This foundational framework sets up the book's core practical premise: since habits operate through this specific cue-routine-reward structure, genuinely changing a habit requires working within this structure, not simply attempting to override it through willpower alone.