How the sense of obligation works

The norm of reciprocity has been found in almost every society studied: you receive, you give back. It's a useful rule: it supports exchange between people who are neither relatives nor friends. You can give first without losing out - people remember what they owe.

The catch is that the rule is triggered by the act, not by your consent. No one asks whether you need a free sample, help moving, or someone else's advice. Once they're given, the tab is already open. And you want to settle it with your body, not your mind: it's mild tension, not a thought.

The person who gives first gets two advantages at once. They choose the moment - and they choose how you will repay them. A small favor opens the door to a disproportionate request: the gift is trivial, but in return they ask for your agreement, time, or silence.

The second lever is reputation. Refusing to repay can earn you a label: ungrateful. It sticks because it calls into question not your taste or manners, but your integrity itself. That's where "but I did this for you..." comes from - the phrase isn't about the past, but about the price being named now.