Rising awareness of mental illness has increased the public’s mental health literacy, with positive implications for help-seeking and destigmatization. We argue that it has also enlarged the public’s concept of mental illness. People have become better at recognizing the presence of mental illness but may have become worse at recognizing its absence. This conceptual expansion fosters unwarranted self-diagnosis, the pathologization of ordinary distress, and unnecessary treatment. It is incumbent on mental health professionals to promote accurate knowledge of mental illness and push back against overly expansive concepts of it.