Psychology says people who can’t stop at one cookie after opening the jar may be responding to more than hunger

You open the cookie jar intending to take just one. A few minutes later, you are reaching for another, then another, wondering how the entire jar suddenly became your responsibility. It can be tempting to describe this as having “no willpower,” but psychology offers a more complicated explanation. Eating behavior is influenced by reward sensitivity, food cues, habit formation, self-regulation, portion norms and dietary restraint. In other words, the decision to eat another cookie does not happen entirely in isolation. The appearance, smell, availability and expected pleasure of the food can all influence what happens after the first bite. A major 2025 review by psychologists Traci Mann and Andrew Ward notes that eating self-control is influenced by reward sensitivity, external eating, emotions, calorie deprivation and environmental cues, rather than being simply a matter of willpower.

Psychology Says The First Cookie Can Activate the Brain’s Reward System