The 10 Investment Mistakes: That Quietly Cost You the Most

The 10 Mistakes at a Glance

The Mistakes in Detail

1. Trying to time the market

The urge to sell before a fall and buy back before a recovery is almost universal — and almost impossible to pull off, because it requires being right twice. Most investors who go to cash in a panic miss the sharpest part of the rebound, which historically arrives without warning and close to the bottom. The cost of sitting out a handful of the market’s best days is enormous, and those days cluster maddeningly near the worst ones. Staying invested through the discomfort is unglamorous, but it beats trying to outguess the market’s timing. As the saying goes, it’s time in the market, not timing the market, that builds wealth.

2. Underestimating the drag of fees

Fees feel small — one percent here, a performance fee there — but they compound against you exactly as returns compound for you, and over decades the leak runs into millions on a sizeable portfolio. The most insidious version is the closet indexer: an active fund charging active fees while quietly hugging its benchmark, so you pay for skill and receive the index minus costs. Know your Total Investment Charge across every holding, and make sure you’re only paying active fees where there’s genuine active management to justify them. We unpack this fully in our guide to active vs passive investing.

3. Letting emotion drive decisions

Fear and greed are expensive advisors. They push investors to buy at the top, when optimism is everywhere and prices are high, and to sell at the bottom, when fear peaks and bargains abound — the precise opposite of what builds wealth. This buy-high, sell-low cycle does more damage to real-world returns than any fund choice ever will. The antidote isn’t to suppress emotion but to remove it from the decision: a written plan you follow regardless of how the headlines feel. We explore the behavioural traps in depth in the psychology of wealth.

4. Putting too much in one bet

Concentration builds fortunes and destroys them — the difference is luck, not skill. Too many South Africans hold a dangerous overweight in a single position: company shares from an employer, one beloved stock, a single sector, or one buy-to-let property carrying half their net worth. When it works, it feels like genius; when it fails, it can be ruinous, and you rarely see it coming. Diversification across companies, sectors, and asset classes is the one free lunch in investing. The same logic applies to property versus shares: a single building in a single suburb is a concentrated bet, however solid it feels.

5. Staying anchored to South Africa

Familiarity feels like safety, but home bias is one of the most expensive habits a South African investor can have. South Africa represents less than 1% of global market value, yet many local portfolios hold the overwhelming majority of their wealth here — in local shares, local property, and a local business besides. That concentrates your financial future in one small, volatile economy and currency, and shuts you out of the world’s best companies. Meaningful offshore exposure isn’t exotic or unpatriotic; it’s basic risk management, which is why we treat offshore investing as a core discipline.

6. Chasing last year’s winner

The fund at the top of the performance tables, the share everyone’s talking about, the hot theme of the moment — the instinct to pile in after a strong run is powerful and usually wrong. Performance chasing means consistently buying high, after the gains have happened, and it’s how investors end up holding last cycle’s winners into this cycle’s losses. Hot tips and recent performance are the worst possible basis for a long-term decision. A sound strategy, followed consistently, will quietly outperform a portfolio that’s forever chasing whatever just went up — including the latest market mania, however convincing the story.

7. Investing without a plan

Plenty of people own investments without ever having made an investment plan. They’ve accumulated a scattering of funds, policies, and tips over the years with no goal, no target asset allocation, and no strategy tying it together. Without a plan, every market move becomes a fresh decision made under stress, and decisions made under stress are usually bad ones. Start at the other end: define what the money is for and when you’ll need it, set an asset allocation that fits, and let that plan — not the news — drive what you buy and hold.

8. Interrupting compounding

Compounding is the most powerful force in investing, and also the most fragile, because it depends entirely on being left alone. Starting late, cashing out during a scare, switching strategies every few years, or dipping into the pot — each one resets the clock and quietly steals the years when growth would have snowballed hardest. The investor who starts earlier and simply stays the course almost always ends up ahead of the cleverer one who keeps interrupting the process. We put real numbers on this in our guide to the fundamentals of smart investing.

9. Confusing activity with progress

In most of life, effort produces results. Investing is the strange exception, where doing less usually beats doing more. Constant tinkering, frequent trading, and reacting to every headline feel productive but rack up costs, trigger tax, and tempt exactly the mistimed decisions that erode returns. The financial media is built to make you feel you must do something — that’s how it holds attention. A good portfolio is mostly a matter of patience punctuated by rare, deliberate adjustments, not a stream of reactions to noise.

10. Ignoring tax

Tax is a cost like any other, and it’s one of the few an investor can legally reduce. Yet many leave real money on the table by ignoring the tax-efficient vehicles available to them — tax-free savings accounts, retirement annuities, and the right ownership structures for larger portfolios. Two investors earning identical returns can end up with materially different outcomes purely on how thoughtfully each used these tools. (Specific limits and rates change, so confirm the current figures at sars.gov.za.) It rarely makes sense to let the most controllable cost go unmanaged.

How to Avoid Them

Notice what nearly all of these mistakes have in common: they’re not knowledge problems, they’re discipline problems. Almost every investor knows, in the abstract, that they shouldn’t panic-sell or chase hot tips or pay bloated fees. The difficulty is doing the right thing in the moment, when fear or greed or boredom makes the wrong thing feel urgent.

That’s where a plan — and often a steady outside hand — earns its keep. A written strategy converts good intentions into a rule you can follow when your instincts are screaming the opposite. And a good advisor’s most valuable role is frequently not picking investments at all, but stopping clients from making these ten mistakes at the worst possible times. As a fee-only firm, we’re paid the same whatever you hold, so our only job is to keep your plan — and your behaviour — on track. If you suspect one or two of these are quietly costing you, that’s usually the most valuable place to start, and we explore the broader case in our piece on DIY investing.