An index fund is an investment that buys a tiny slice of hundreds or thousands of companies at once, instead of betting on one. There are two ways to invest: bet everything on the single company you're sure will moon, or quietly own a slice of all of them. Over 20 years, owning everything usually wins — and it isn't close. Even the professionals, with their suits and fees, mostly fail to beat the index.
Because picking the future winner is far harder than it looks, and the cost of being wrong is steep. Owning the whole market means you automatically hold every winner without having to guess. In the simulator, betting $10,000 on one random company is a gamble; the index quietly turns $10,000 into about $39,000 over 20 years, every time.
Fees are a silent drag that compounds against you, the same way returns compound for you. Index funds are typically very low-cost because no expensive manager is trying to outsmart the market. Keeping fees tiny is one of the few free wins in investing.
Don't hunt for the needle — buy the haystack. Own the broad market, keep fees low, and let time compound it. It's deeply boring, and boring is, annoyingly, the approach that tends to win.