Why do patients feel obligated to repay a favor even when they don't like the person? Because the debt obligation lives underneath the relationship, not on top of it. The strange truth researchers found is that reciprocity fires even when you cannot stand the other person. The favor still needs repaying. I think about the story of Ethiopia and Mexico. Italy invaded Ethiopia in the 1930s, Mexico sent aid, and fifty years later after a Mexico City earthquake, a country that had been poor for generations sent money back. The debt outlasted everything. That is how deep this runs in people. [...]