David Rosenhan, a professor of psychology and law at Stanford University, conducted an interesting experiment.
He selected eight completely normal people: three psychologists, a psychiatrist, a pediatrician, an artist, a housewife and a graduate student.

All of them turned to psychiatric clinics as people who “are concerned about their mental health.” Everyone told the truth about themselves and their condition, except for one detail – they allegedly heard voices saying “empty”, “deaf”, “stitch”. The doctors considered them mentally ill. They were all sent to clinics.

Immediately after hospitalization, the doctors told them they felt great and no more voices were heard. Everyone was on treatment for 52 days and behaved like normal people.

Results of:
According to the results of treatment, seven were diagnosed with schizophrenia, and one was diagnosed with manic-depressive psychosis.
After being discharged from the clinic, their condition was described by doctors as “improved,” “in remission,” but no doctor thought they had recovered.
None of the doctors knew they were completely healthy. They were “divided” by patients – they decided that they were faced by journalists or hospital inspectors.

After the publication of the results of the experiment, all psychiatric clinics questioned them, saying that such gross mistakes were impossible. Professor Rosenhan proposed to repeat the experiment, saying that he would send to them some more imaginary patients.

The clinics carefully diagnosed the following 193 patients, and 41 of them were diagnosed as “pseudopathic”.
In fact, the professor did not send a single person to the clinic.