A lot of different cultures claim to have the monopoly on feeling guilt; I've personally been to dinner parties where Jewish and Catholic guests argued for hours about their religion's supreme handle on the emotion. But when it comes to understanding why we feel guilt, things get more complicated. Guilt, it turns out, is a complicated emotion with intriguing ramifications for how we interact with others and interpret moral codes — and that's led to several competing ideas about why it has developed and what purpose it really serves in human psychology.
When it comes to defining guilt, it needs to be disentangled from another similar emotional experience: shame. According to a 2014 review of neurobiology in the brain, the common way of distinguishing these two emotions is through their social ties: "While the feeling of shame implicates the presence of other people, guilt can arise and persist without others." Guilt, in other words, can be a private emotion about transgressing or doing something wrong, while shame is about our concern at the opinions and disapproval of others when we've done something wrong.
Guilt is also a hugely powerful emotion, one that we actually feel physically; Princeton scientists found in 2013 that we do genuinely feel "heavy" with the weight of our deeds when we're experiencing guilt.
So why on earth does guilt exist (beyond giving our parents an emotional superpower that helps them manipulate us into coming home for Thanksgiving)? Researchers have some ideas.