Every habit runs on a three-part loop

Duhigg's foundational model is the habit loop: a cue (a trigger, like a time of day or a feeling) sets off a routine (the behavior itself), which delivers a reward that the brain then associates with the cue, cementing the loop for next time. Crucially, once a behavior becomes habitual, the decision-making part of the brain goes quiet — the basal ganglia takes over, which is why habits feel automatic and why we often can't explain why we did something.

Duhigg opens with lab rats navigating a T-shaped maze for a chocolate reward; brain activity that starts out frantic and decision-heavy on the first run gradually flatlines into near-silence after enough repetitions, even though the rat still runs the maze perfectly. The same flattening happens in humans learning to drive or brush their teeth — competence rises while conscious attention drops to near zero.

This loop structure is also why habits are so hard to delete outright — the neurological pathway never fully disappears, it can only be overridden by inserting a new routine into the same cue-reward bracket.

Takeaway: to change a habit, keep the cue and reward, and replace only the routine in between.