This installment of Yale's Understanding Medical Research: Your Facebook Friend Is Wrong explains surrogate endpoints, the stand-in measurements researchers use when the outcome they actually care about, such as death or disability, would take too long or too many patients to observe directly. The lecturer walks through examples like cholesterol levels standing in for heart attacks and tumor shrinkage standing in for survival, showing why a treatment that improves the surrogate does not always improve the outcome patients actually care about. The talk covers how surrogate endpoints get validated, where drug trials have been misled by them, and what questions a careful reader should ask when a headline cites a study built on one. It is a short, focused segment aimed at helping non-specialists read medical news and clinical trial claims more critically, using plain language rather than technical statistics.