Personal finance Twitter has done a remarkable job convincing twenty-somethings that not buying index funds is financial malpractice. Compound interest! Time in the market! The math is technically right and the advice is still wrong for most of the people receiving it. There’s a sequence to building a financial foundation, and stocks come well after several other items most beginners haven’t checked off. Skipping straight to investing while the prerequisites are unfinished is how people end up selling at the bottom.
High-interest debt eats every realistic stock return
The S&P 500’s long-run average return is roughly 10% nominal, around 7% after inflation. Credit card APRs sit between 20% and 30%. Carrying a credit card balance while buying index funds is the financial equivalent of running a faucet while bailing out a boat. Even relatively cheap debt — a 9% personal loan, an 11% car loan — is a guaranteed return on payoff that index funds can’t reliably match. Paying off high-interest debt isn’t a detour from investing; it’s the highest-confidence investment available, and it’s risk-free.
No emergency fund means forced selling at the worst time
Stocks are volatile in the short run. Anyone who started investing in late 2021 watched 25% disappear in 2022 before it came back. That’s fine if you don’t need the money. It’s a disaster if your car transmission dies and the brokerage account is your only liquidity. Forced selling during drawdowns turns a paper loss into a permanent one and is the single most common way retail investors actually lose money. A three-to-six-month expense buffer in a high-yield savings account is the precondition that makes a stock portfolio survivable.
Income instability changes the calculus
If your job, hours, or contract income could meaningfully change in the next year, the case for tying up money in equities weakens further. Job loss combined with a market drawdown is the worst-case scenario, and it’s not unusual. Cash reserves, marketable skills, and a low fixed-cost base are arguably better “investments” for someone in their first few years of earning than a brokerage balance. The compounding argument assumes you don’t have to interrupt the compounding, and most early-career interruptions come from cash crunches.
The bottom line
Index funds are a great default — once the foundation is in place. The order is roughly: high-interest debt cleared, an emergency fund built, employer 401(k) match captured, then taxable or IRA investing. Skipping ahead because compound-interest charts feel motivating is a way of optimizing one variable while ignoring the variables that actually determine outcomes. The market will still be there in eighteen months when the prerequisites are done, and you’ll be a meaningfully better investor for having done them. Buying stocks isn’t the responsible adult move; building the buffer that lets you hold them through a downturn is.
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