Today’s Eponymy in August is the Ben Franklin effect.
In the eponymous’s own words, “He that has once done you a kindness will be more ready to do you another, than he whom you yourself have obliged.”
In a more modern language and analysis, there isn’t a causative effect from a person liking you to a person doing favors for you. In fact, it seems to be bidirectional; if you do favors for someone, you tend to like them more (the inverse is also true; if you hurt someone you like them less to lessen the impact in your own mind of the injury you caused). It’s theorized but not proven that our justifying minds do this to avoid the cognitive dissonance that arises from doing favors for people who we don’t care for.
Franklin was one of history’s greatest polymaths, having his hand in writing, publishing, science, invention, education, music, chess, urban planning, government, and diplomacy. He himself used this principle once when he needed the support of a rival legislator in the Pennsylvania statehouse. Franklin appealed to the vanity of the rival about his sizable library by requesting to borrow a rare book from it. From this small favor, Franklin got his foot in the door, so to speak, and turned the rival to a lifelong friend.