Understanding Schizophrenia: Symptoms, Causes, and Treatment: Schizophrenia is a severe mental disorder that affects a person’s perception of reality, causing delusions and abnormal thinking. According to an article published by MentalHelp, roughly 1.2% of the United States population is affected by schizophrenia. While the disorder is not very common, schizophrenia is considered a chronic illness that can produce serious symptoms.