A mistake will set you back further than a missed optimization
A year into her first job, she logged into her 401(k) to bump up her contribution and noticed something off. The money she’d been proudly setting aside every paycheck had been sitting in cash the whole time — earning nothing, compounding nothing, for fourteen months. She hadn’t done anything reckless. She had just missed a step nobody mentioned.
Almost every expensive beginner mistake works like that: not a bad bet, but a silent gap in something you thought you’d handled. The fear, when you’re new to this, usually isn’t picking the second-best fund. It’s doing something costly without realizing it and finding out years later, when it’s harder to undo.
Here’s the reassuring part: the costly mistakes are a short, well-known list. Avoid these six and you’re already ahead of most people, no advanced knowledge required. None of them ask you to predict anything or beat anyone — they’re about not handing money away.
The six roughly follow the money order of operations: capture free money, clear expensive debt, use the right accounts, then behave well once you’re invested. Read the numbers as a tour, not a ranking.
Leaving the employer match on the table
A 401(k) match is part of your pay, not a bonus: your employer adds $0.50 to $1 for every dollar you put in. Skip it and you turn down an instant 50–100% return that would grow on itself for decades.
The fixSet your contribution high enough to collect every matching dollar before you save anywhere else — usually a percentage you change in your payroll or HR portal.
Read: the 401(k) guidePaying off low-interest debt before high-interest
Putting extra money toward a student loan at 4% APR while a credit-card balance at 24% keeps growing costs you the gap between those rates every month.
The fixAttack the highest rate first — that's the avalanche method. When two rates are about equal, knock out the smallest balance first for a quick win (the snowball).
Read: the debt-payoff guideInvesting in a regular account before the tax-advantaged ones
Money in a regular brokerage account gets taxed on its growth. Filling one while tax-advantaged accounts like a Roth IRA or HSA sit empty hands the IRS a cut you could have kept.
The fixFill the tax-advantaged accounts first — the match, then a Roth IRA (and an HSA too, if you're on a high-deductible health plan) — and put anything left over in a regular account.
Read: the order of operationsTrying to time the market — and selling when it drops
A downturn feels like the moment to get out, but selling turns a temporary dip into a permanent loss. You rarely buy back in time, and missing just the best handful of days guts a decade of returns.
The fixWhen the market drops, stocks are on sale — that's the time to stay the course, keep buying on schedule, and not panic-sell.
Read: when the market dropsGambling on hot individual stocks instead of diversifying
A hyped-up stock or a coworker's hot tip can crater and take a chunk of your savings with it. A single company can go to zero; a fund that owns the whole market never has.
The fixOwn the whole market through a low-cost index fund and let broad growth, not a lucky pick, do the work.
Read: what you actually ownBuying whole life insurance as an investment
Whole life insurance bundles insurance with investing, which usually means high fees and thin returns on both. Much of your early premium goes to the agent's commission, not your savings.
The fixBuy cheap term insurance for the coverage, and invest the difference yourself in a Roth IRA or 401(k).
Read: the whole-life pitchThe flip side: what to do instead
Notice that every fix points back to the same handful of moves — capture the employer match, clear high-interest debt, fill the tax-advantaged accounts, buy a broad index fund, and then leave it alone. There’s nothing exotic on the list, and there’s nothing exotic in the fixes either.
That sequence has a name and a step-by-step roadmap. If this page told you what not to do, the order of operations tells you exactly what to do next.
The positive version of this whole page is the Money Order of Operations — the same moves, in the order that gets the most out of every dollar.