Most accounts of the discovery of "pleasure" circuits in the brain begin with the observation by James Olds and Peter Milner in 1953 that electrical brain stimulation can condition operant responses in rats. Less well-known, pleasurable brain stimulation was previously observed in schizophrenic patients by Robert Heath. However, Heath failed to recognize the significance of this observation, at least in part, because of preconceived notions he held about the etiology of schizophrenia. This episode in the history of neuroscience illustrates the importance of sagacity in serendipitous scientific discoveries. It also shows that "mental preparedness" can be an obstacle to progress.