In January 2023, the fiftieth anniversary passes of David Rosenhan’s article On being sane in insane places appearing in the prestigious journal “Science”. This publication has become one of the most influential psychiatric papers of the second half of the 20th century, achieving 1,276 citations up to mid-2022. In the article, eight healthy persons are described, who came to psychiatric hospitals in the USA, reporting auditory hallucinations. They were all admitted, mainly with suspected schizophrenia, and ordered pharmacological treatment. Their stay ranged from 7–52 (mean 19) days, even though after the admission they did not confirm the symptoms. The article spotlighted an unjustified diagnosis of mental illness, resulting in psychiatric hospitalization in unfavorable conditions. Its consequences were manifold. It augmented the process of psychiatric deinstitutionalization and provided food for anti-psychiatric movements and humanistic psychiatry. However, it did accelerate the inception of an objective system of psychiatric diagnosis in the form of the 3rd edition of the Diagnostic and Statistical Manual (DSM-III), released in 1980. Susannah Cahalan’s book The great pretender, published in 2019, undermines the reliability of the article. Based on many interviews and Rosenhan’s notes, she pointed out many faults of the experiment. She was not able to retrospectively confirm the identities of the majority of participants, nor to receive the essential information from “Science”. On the fiftieth anniversary of the article, its cognitive value for an objective diagnosis of mental illness and the role of psychiatric hospitalization as well as the negative consequences in the form of a drastic reduction of psychiatric beds in the USA are emphasized.