A study by American Psychologist Rosenhan "On being sane in insane places" demonstrated that psychiatrists cannot reliably distinguish between people with a genuine mental illness and people pretending to have one. Rosenhan sent accomplices to Hospitals, all with the instruction that they complain of one symptom, hearing the word "Thump". All were institutionalized and labeled as being sufferers of a variety of conditions "in remission" upon their discharge. There was much fury from the psychiatric establishment when these results were made public. One psychiatrist challenged Rosenhan to send accomplices again, confident that he could spot them. Rosenhan agreed, and some time later the psychiatrist proudly contacted Rosenhan in the belief that he had found them all, to which Rosenhan responded that he hadn't sent a single one that time. Rosenhans' term for persons in a situation of being mistaken for insane was "pseudopatient"and the subtext of his study is that any social faux pas, intentional or not, could be misinterpreted as a psychiatric symptom by a psychiatrist.
According to the Adam Curtis documentary "The Trap: What happened to our dream of freedom?" the NHS, and other public services, under New Labour introduced a system of targets to motivate staff, in line with the theories of John Nash as interpreted by Alain Enthoeven. The documentary highlights the problem that staff could simply falsify the paperwork to create the illusion of targets being met in order to keep their jobs. This would include misdiagnosing someone. John Nash had schizophrenia.
Due to the psychological phenomenon of Confirmation Bias, a psychiatrist might see one symptom of a Condition in a patient and then assume that the patient must have all the other symptoms.
Not believing that one has a mental illness is a psychiatric symptom: "Lack of insight" or "Anosognosia". However, sane people also believe that they do not have a mental illness.
In 2015 a black woman, a banker, was detained by Brooklyn police for dancing to music in her car at a stoplight. She was not charged and was told to collect her car the next day. When she returned, she was taken to a Psychiatric Ward, stripped and medicated because the Police could not accept that the BMW belonged to her. She was held for eight days and went on to sue for damages.