The Ben Franklin effect is a psychological finding:
A person who has done someone a favor is more likely to do that person another favor than they would be if they had received a favor from that person. Similarly, one who harms another is more willing to harm them again than the victim is to retaliate.
In the words of Benjamin Franklin, who famously observed the effect and for whom it is named, “He that has once done you a Kindness will be more ready to do you another, than he whom you yourself have obliged.”
This perception of Franklin has been cited as an example within cognitive dissonance theory, which says that people change their attitudes or behavior to resolve tensions, or “dissonance”, between their thoughts, attitudes, and actions. In the case of the Ben Franklin effect, the dissonance is between the subject’s negative attitudes to the other person and the knowledge that they did that person a favor.
Ben Franklin when he served in the Pennsylvania legislature in the 18th Century. In his autobiography, he explains how he dealt with the animosity of a rival legislator:
“Having heard that he had in his library a certain very scarce and curious book, I wrote a note to him, expressing my desire of perusing that book, and requesting he would do me the favour of lending it to me for a few days. He sent it immediately, and I return’d it in about a week with another note, expressing strongly my sense of the favour. When we next met in the House, he spoke to me (which he had never done before), and with great civility; and he ever after manifested a readiness to serve me on all occasions, so that we became great friends, and our friendship continued to his death.”