The mental model this study illustrates is called reciprocity, whereby you tend to feel an obligation to return (or reciprocate) a favor, whether that favor was invited or not. In many cultures, it is generally expected that people in social relationships will exchange favors like this, such as taking turns driving a carpool or bringing a bottle of wine to a dinner party. Quid pro quo (Latin for “something for something”) and I’ll scratch your back if you’ll scratch mine are familiar phrases that relate to this model.
