True or false: Eight glasses of water a day are mandatory for staying hydrated. Vitamin C protects you from catching a cold. Frequent snacking is the quickest way to bust your diet. Natural foods are always better for you. You hear advice like this all the time. But what do these four nuggets of so-called medical wisdom have in common? They're all myths, half-truths, and misconceptions—pieces of information so familiar we take them for granted without truly considering the scientific truth behind them.