If we think of having a diagnosable mental illness as being under a tent, the tent seems pretty big. Huge, in fact. How did it happen that half of us will develop a mental illness? Has this always been true and we just didn’t realize how sick we were—we didn’t realize we were under the tent? Or are we mentally less healthy than we were a generation ago? What about a third explanation—that we are labeling as mental illness psychological states that were previously considered normal, albeit unusual, making the tent bigger. The answer appears to be all three.