Harvard psychology professor Dan Shapiro has spent the last two decades trying to uncover what emotionally charged conflicts -- from marital spats to high-stakes political disputes -- have in common. He found that the conflicts that feel most intractable are those that threaten a person's identity and trigger a "tribal mindset." Shapiro joins Forum to talk about his new book, "Negotiating the Nonnegotiable: How to Resolve Your Most Emotionally Charged Conflicts."