Taking a deep breath or two to relax in and of itself isn’t new. Many people take a few deep breaths when they’ve feeling overcome by stress, and the adage, “just breathe” appears on everything from billboards to t-shirts. Deep breathing, often referred to as “belly or diaphragmatic breathing,” is incorporated in many different mind–body therapies. There is one fundamental problem with breath modification techniques, however. The majority of people are not fully aware of their lungs’ capacity. Consequently, they fail to inhale or exhale fully. Why is this the case?