To us, Osler's proclamation expresses the obvious truth that medical knowledge is grounded in an eminently rational science. The very fabric of our day-to-day clinical experience rests on the faith that what we have learned and what we base patient-care decisions on is, in fact, true. We assume our own assumptions have undergone rounds and rounds of objective scrutiny from the academic community and from government oversight agencies.
But sometimes we encounter the unexpected. Sometimes, somehow, the constellation of the patient's symptoms do not fit any algorithm for disease we can recall. Or the pathology resists what should have been definitive treatment. At times this is a superficial error of judgment, at other times these gaps in our understanding testify to a deeper incongruity in the pat elements of knowledge we work with. For instance, Dr Anthony Fauci's group at the National Institutes of Health recently discovered that immunization of HIV-1—infected individuals with a