The Power of Habit: Why We Do What We Do and How to Change

by Charles Duhigg

Since The Power of Habit was published, there’s been an explosion of research looking at mental habits and, in particular, habitual behaviors like gratitude.2 In one study published in 2016, for instance, researchers at Indiana University scrutinized 293 people who had come to the University’s mental health offices looking for counseling.3 All of the participants received therapy and, in addition, the researchers instructed a third of them “to write one letter of gratitude to another person each week, for three weeks.” Another group was instructed to write introspectively about their deepest thoughts and experiences. A third group was not assigned any writing tasks. Twelve weeks later, when the researchers polled all the participants, they found the grateful letter writers “reported significantly better mental health” and, on tests of well-being, indicated they had improved at as much as twice the pace of the other groups. This was particularly interesting because, in most cases, the letter writers had never sent their letters. They had simply scribbled their gratefulness and then set the cards aside.