Are you familiar with the Law of Reciprocity? This is the psychological perception of obligation when we receive a gift, favor, or act of goodwill from someone else. The book The Essentials of Power, Influence, and Persuasion (Harvard Business School Press, 2006, p. 50) describes the law like this:
I’ve been aware of the law of reciprocity for some years now (since I did some reading on persuasion psychology) and I’m quite self-aware of its power over me. Surprisingly, that awareness doesn’t necessarily diminish its power.
Just today I walked into the grocery store and a friendly elderly gentleman was giving away free samples of his smoked sausage. In the moment I knew that walking over and trying a piece would immediately put me at risk of feeling obliged to buy a link, but alas, I went anyway. After trying the first piece he encouraged me to try the chili flavor as he described that their company had just started in December, locally produced with no GMOs or MSG or blah blah blah.
By this time it was too late. I yielded to the path of least resistance and surrendered to the pull of this perceived obligation by placing a link of sausage into my basket.