The powerful placebo and the Wizard of Oz.

Some myths really ought to be true. We react with surprise and pleasure when we encounter them and then believe them when they neatly and comfortably help to explain some confusing aspect of our world. Thereafter, evidence against them is unwelcome and not to be trusted. But some such myths are flawed and misleading. John Snow has been widely credited with stopping a cholera epidemic in 1854. He noticed that the disease was prevalent among Londoners who drank from a well supplied by one water company but not among those who drank from the well of another company, and he . . .