In1973 the journal Science published an article titled "On Being Sane in Insane Places." It described an experiment in which eight "fake" patients with no history of mental illness went undercover and checked themselves into a few psychiatric hospitals across the United States. All of them had the same complaint: they told medical staff that they regularly "heard voices." Apart from this fabrication they behaved normally and recounted their own (normal) past experiences and medical histories.

Nonetheless, all of them were diagnosed as schizophrenic (except one, who was diagnosed with "manic-depressive psychosis"), hospitalized for up to two months, and prescribed antipsychotic medications (which they did not swallow). Once admitted to the mental wards, they continued to speak and behave normally; they reported to the medical staff that their hallucinated voices had disappeared and that they felt fine. They even kept notes on their experiment, quite openly (this was registered in the nursing notes for one of the fake patients as "writing behavior").

This experiment, designed by David Rosenhan, a Stanford psychologist and one of the fake patients, found that the single symptom of "hearing voices" could suffice for an immediate, categorical diagnosis of mental illness even in the absence of any other symptoms or abnormalities of behavior. In other words, "hearing voices" could only have one explanation—you're crazy.

Possible Preaching Angles: Of course mental illness is a reality, but at times smart people in our society are quick to judge that Christians who hear from God are also crazy or deluded.