Topic: Investment · Type: Evergreen · Reading time: ~8 min

The S&P 500 returned 25% in 2024. The average equity investor made 16.5%. That gap — nearly 8.5 percentage points — wasn't caused by bad luck or a brutal market. According to DALBAR's annual investor behaviour study, it was almost entirely self-inflicted: withdrawals timed just before rallies, panic selling, late re-entries. More effort, less return.

This happens every year. For the past 15 consecutive years, the average equity investor has underperformed the index they were invested in. Not because the market is rigged. Because the biggest investing mistakes beginners make have nothing to do with picking stocks, and everything to do with behaviour, fees, and a few surprisingly easy-to-miss fundamentals.

Here's what's actually costing people money — and what to do instead.

Mistake 1: Treating investing as an event, not a process

Most beginners approach investing the way they approach a purchase: research, decide, buy, done. But the market doesn't care about your entry point. What matters is whether you stay invested when things get uncomfortable — and things will always get uncomfortable.

In March 2020, markets fell 34% in 33 days. Millions of investors sold. By August 2020, the major indices had fully recovered. The people who panicked didn't just miss the rebound — they locked in losses and then had to decide when to get back in, which is an even harder problem. This pattern repeated in 2022, and again during the tariff-driven volatility of early 2025, which was followed by record highs just weeks later.

The fix isn't willpower. It's structure. Automating your investments — setting up a monthly transfer into a diversified fund regardless of market conditions — removes the decision entirely. You stop trying to time anything. You just accumulate. This approach, dollar-cost averaging, is one of the most well-documented strategies for reducing the emotional cost of investing, and it requires zero market expertise to execute.

Mistake 2: Ignoring fees (because they seem small)

A 1% annual management fee sounds like almost nothing. Over 30 years, on a £100,000 portfolio earning 7% annually, it costs you roughly £142,000 in lost growth compared to a 0.5% alternative. That's not a rounding error — it's a second portfolio you never got to build.

The fee gap between actively managed funds and passive index trackers is real and persistent. Many actively managed funds charge between 0.75% and 1.5% annually, while a globally diversified ETF tracking the MSCI World or S&P 500 typically costs between 0.07% and 0.25% — and has outperformed the majority of active funds over long time horizons. Morningstar's 2025 Mind the Gap report found that over the decade to December 2024, investors forfeited approximately 15% of their total potential returns just from behavioural and fee drag combined.

The place to start: look up the expense ratio (also called the TER — Total Expense Ratio) on every fund you hold. If it's above 0.5% and it's not a specialist sector fund with a clearly documented reason for the cost, it's worth questioning. ETFs for beginners covers how to find low-cost options across different markets and brokers.

Worth knowing: In the EU and UK, brokers are required to show you an annual cost disclosure — often called a "cost and charges" statement — that itemises what you actually paid. Most investors never open it. Open it.

Mistake 3: Confusing diversification with safety

"I'm diversified" is one of the most frequently misused phrases in personal finance. Holding five tech stocks isn't diversification. Holding a US equity fund and a Nasdaq ETF isn't diversification — they're two bets on the same thing.

Real diversification means spreading across asset classes (equities, bonds, real estate), geographies (not just the US), and sectors. When one part of the portfolio drops, another part typically cushions it. This doesn't eliminate volatility — nothing does — but it significantly reduces the risk of a single event wiping out a large portion of your wealth.

For most beginners, a single globally diversified index fund does this automatically. A fund tracking the MSCI All Country World Index, for example, holds positions in thousands of companies across 47 countries. You're not betting on any one region's economy or any one company's management decisions. You're betting on human economic activity broadly — which, historically, has been a sound bet.

If you want to understand whether a diversified portfolio built from scratch is right for your situation, the structure matters as much as the individual holdings.

Mistake 4: Starting later because the time never feels right

There's always a reason to wait. The market is too high. There might be a recession. Interest rates are uncertain. Geopolitics are messy. These things are always true, in some form, because they're always true. There has never been a moment in market history where the future was unambiguously clear.

The cost of waiting is concrete. A £1,000 investment at age 22, growing at 8% annually, becomes approximately £21,700 by age 62. The same £1,000 invested at 32 becomes around £10,000. That decade of delay doesn't just cost the initial growth — it compounds the loss across every subsequent year. Starting smaller and earlier nearly always beats waiting to invest a larger sum.

This is the mistake that's hardest to undo because, unlike a bad fund choice or a high-fee platform (both of which can be corrected), lost time can't be recovered. How compound interest works makes this maths visible in a way that tends to change how people think about urgency.

Mistake 5: Chasing what worked last year

In 2023, the Magnificent Seven — Alphabet, Amazon, Apple, Meta, Microsoft, Nvidia, Tesla — drove a huge proportion of S&P 500 returns. Investors poured money into these stocks and into US-heavy funds in 2024. Then, in early 2025, exactly those positions were hit hardest when sentiment shifted.

This isn't a new pattern. Investors consistently pour money into whatever just performed well, and withdraw from whatever just underperformed. DALBAR found that in 2024, the average equity investor withdrew 3.23% of assets — the ninth consecutive year of net outflows — with the largest exits occurring just before major gains. Their "Guess Right Ratio" — the frequency with which investor timing was actually correct — fell to 25%. That means three out of four timing decisions made things worse.

The antidote isn't sophistication. It's a pre-set allocation — a target percentage in equities, bonds, and other asset classes — that you rebalance back to annually regardless of what's been performing. You end up selling high and buying low automatically, not because you predicted anything, but because the system is designed to do it for you.

What this means for you

None of the five mistakes above require advanced knowledge to avoid. They require a clear structure, low-cost vehicles, and the discipline to not override the plan when headlines get loud.

If you take one practical step from this: check the expense ratio on every fund you currently hold. If any of them are above 0.5% without a clear justification, that's the first thing to fix. Not because fees are the only issue — but because it's the one variable fully within your control, regardless of what markets do next.

The investors who consistently build wealth over decades aren't the ones who made the best calls. They're the ones who made the fewest costly mistakes.