Some people, especially those in public service, perform admirable feats: Think of health-care workers fighting to keep patients alive or first responders arriving at the scene of a car crash. But the emotional weight can become a mental burden. Research has shown that emergency personnel are at elevated risk for mental health challenges like post-traumatic stress disorder. How can people undergo such stressful experiences and also maintain their well-being?A new study from the McGovern Institute for Brain Research at MIT revealed that a cognitive strategy focused on social good may…