If I’m in pain because I’m feeling your pain, there is a much easier way to make my pain go away than helping you—I can turn my head and stop thinking of you; the empathic connection is broken, and I’m right as rain. Then there’s Batson’s research, which shows that people tend to help even when escape is readily available. This is a problem for the selfishness theory of the power of empathy and is more consistent with the view that empathy motivates good behavior (when it does) by exploiting positive sentiments that are already present.
