The main thing a clinical trial was designed to measure — the result that actually determines whether the trial succeeded or failed.A trial that fails its primary endpoint has not demonstrated efficacy for that indication, regardless of secondary endpoint results. Secondary endpoints in a failed trial are hypothesis-generating, not confirmatory — they can justify designing a new trial, but they do not rescue the primary failure. This distinction is frequently ignored in community reporting of trial results: "the trial failed but secondary endpoints were promising" is often presented as evidence of efficacy. It is not.