Why does a broad index fund usually beat picking individual winning stocks?

Buying a broad index fund means owning a tiny piece of hundreds or thousands of companies at once, so a few losers barely dent you while the market's overall growth carries you forward. Picking individual stocks, by contrast, requires you to be right repeatedly, and research from S&P and others consistently shows the majority of professional active managers fail to beat their index over long periods. Market returns are also concentrated: a small handful of huge winners drive most of the gains, and missing them by holding the wrong few stocks devastates your results. An index fund guarantees you own those eventual winners. It's not that individual stocks can't work, but for most people the boring, diversified, low-cost index fund delivers better odds and far less stress. Own the haystack instead of hunting for needles.