That heading is the title of a book (1) which presents comprehensive, soundly sourced documentation that 11 common beliefs about medical matters are wrong: about aspirin, low-carb diets, cholesterol, blood pressure, alcohol, exercise, radiation, mammograms, fluoridation, cancer treatment, and chelation therapy. The book was self-published, but the author publicized it at many medical meetings and told me that sales exceeded 20,000. That author had been a valued friend, an organic chemist who worked for a long time at the former University of the (Health) Sciences in Philadelphia.
I think the significant fact about masking was the fact that mask mandates were a gigantic and expensive effort for something that could not be shown to be of benefit and with lots of anecdotal reports that they were ineffective at stopping the spread of respiratory viruses. One could not help but believe that the true purpose was not disease prevention but anxiety production to facilitate vaccine uptake. One of the biggest medical myths of all time is the utility and safety of vaccines, especially those given to children. The book "Turtles All the Way Down: Vaccine Science and Myth" is a thorough demolition of that myth. One of the most shocking facts is that none of the vaccines on the childhood schedule has ever been tested against a true placebo, therefore, the actual risks of the vaccines are unknown. Nor has the effect of the whole vaccine schedule ever been tested with a vaxxed vs. unvaxxed study by the government authorities. There have been several small scale retrospective studies by non-government investigators that have uniformly shown significant statistical associations between vaccination and chronic disease, which is likely the reason no government agency will do such a study (or, if done, will not publicize the results).