One of the biggest contributors to our happiness is something we barely pay attention to: the voice inside our own heads. As psychologist Ethan Kross describes in his new book “Chatter: The Voice in Our Head, Why It Matters, and How to Harness It,” that voice is constantly analyzing the situations we’re in, reflecting on the past and future, and telling us who we are. While sometimes friendly and optimistic—it’s OK, everything’s going to work out!—it can also be critical and downbeat. Our inner voice can berate us for mistakes or decide our life is ruined. It can ruminate on negative emotions and experiences, dredging them up without any kind of constructive resolution. According to Kross, there are three main ways we can turn down the chatter in our heads: shifting our perspective so we’re not so immersed in our problems, talking with others to get support, and changing the environment …