Behavioural finance research has produced one of the most uncomfortable findings in investing: the average investor consistently underperforms the very funds they are invested in. Not by a little — by an average of 3.5% per year, according to JP Morgan. Over twenty years, that gap doesn’t just compound. It quietly halves the wealth you would otherwise have built.
The culprit isn’t volatility. It isn’t fees or fund selection or bad luck. It’s the decisions investors make in response to those things — selling when markets fall, piling in when markets rise, moving to cash when uncertainty peaks, and holding on to poor investments too long because selling would mean admitting a loss. These are not irrational impulses. They are entirely human ones. But they are also expensive.
Understanding why we make these decisions — and what to do about them — is one of the most practical things an investor can learn. This article draws on the core concepts of behavioural finance to explain the biases that undermine long-term returns, and what a structured approach to investing actually looks like in practice.
Key Definitions
Behavioural Finance
A field of economics that studies how psychological factors — emotions, cognitive shortcuts, and social influences — affect financial decisions. It challenges the assumption that investors act rationally, and explains why markets can be persistently inefficient.
Cognitive Bias
A systematic pattern of thinking that deviates from rational judgement. In investing, cognitive biases cause investors to misinterpret information, overweight recent events, and make decisions based on emotion rather than evidence.
Loss Aversion
The tendency to feel the pain of a loss more intensely than the pleasure of an equivalent gain. Research by Kahneman and Tversky found that losses are psychologically about twice as powerful as gains — which explains many of the most damaging investor behaviours.
The Behaviour Gap
The measurable difference between the return a fund delivers and the return the average investor in that fund actually experiences, due to poorly timed decisions. JP Morgan’s research consistently puts this gap at around 3–4% per year.
Why Money Is Personal
Our relationship with money is formed long before we make our first investment decision. The financial environment we grew up in — whether money was abundant or scarce, a source of security or tension, something discussed openly or treated as taboo — shapes the beliefs and behaviours we carry into adulthood.
For some, money means freedom. For others, it’s associated with anxiety, guilt, or status. These associations are rarely examined consciously, but they show up clearly in how people make financial decisions: whether they take on risk or avoid it, whether they invest early or procrastinate, whether they hold on to losing positions out of stubbornness or exit winning ones too soon.
This matters because successful investing isn’t just a technical exercise. It requires a degree of self-awareness that most investment advice doesn’t address. You can have the right portfolio and still sabotage your own outcomes — if your emotional responses to markets override the strategy.
The Real Cost of Behavioural Mistakes
The JP Morgan asset management research referenced earlier is worth dwelling on. The average investor underperforms their own funds by approximately 3.5% annually — not because of fees, and not because they chose bad funds. Because they made poorly timed decisions: selling during downturns, buying into rallies, switching funds after a period of underperformance, or sitting on the sidelines waiting for conditions to improve.
To put that in concrete terms: if two investors each started with R1 million in an identical 60/40 portfolio earning an average of 8.5% per year, but one made behavioural decisions that reduced their net return to 5%, the outcomes after twenty years would look like this:
| Scenario | Annual Return | Value after 20 Years |
|---|---|---|
| Disciplined investor | 8.5% p.a. | R5,110,000 |
| Behavioural investor | 5.0% p.a. | R2,650,000 |
| The behaviour gap | 3.5% p.a. | R2,460,000 less |
That R2.46 million difference represents the compounded cost of emotional decision-making. Both investors held the same fund. One stayed invested. The other didn’t — or at least, not consistently. All figures are illustrative, but they reflect the scale of the problem accurately.
It is also worth noting that this gap is largely invisible to the investor experiencing it. Every exit feels justified at the time. Every re-entry feels like a fresh start. The cost only becomes apparent in retrospect, when you look at what the fund delivered versus what you actually received.
The Psychology of Market Cycles
Markets do not just move in price. They move in sentiment. And sentiment follows a remarkably consistent pattern — from the cautious optimism of a recovery, through the excitement of a rally, to the euphoria of new highs, and then the disbelief, panic, and despondency of a correction. Each stage comes with its own emotional pull, and each pull tends to push investors toward the wrong decision.
The insidious part of this pattern is that it feels rational at each stage. Investing more feels sensible when markets are strong — things are clearly working. Pulling back feels sensible when markets are falling — why hold on? But these instincts are precisely inverted from what good investing requires. The best time to add to a portfolio is usually when it’s most uncomfortable to do so.
After the strong global market returns of 2023 and 2024, many investors are sitting somewhere between “excitement” and “thrill” on that cycle. That’s not a reason to panic — but it is a reason to stay deliberate. Market cycles are always in motion, and a one-year snapshot of strong returns is not a guarantee of what comes next.
Six Biases That Undermine Investment Returns
Behavioural finance has identified dozens of cognitive biases relevant to investing. These six are the most consequential — and the most common among otherwise sophisticated investors.
1. Loss Aversion
Losses register more powerfully than equivalent gains. An investor who watches their portfolio fall by R100,000 will feel that loss more acutely than they felt the corresponding R100,000 gain. This asymmetry drives two of the most costly investment behaviours: holding on to underperforming investments too long (because selling would crystallise the loss), and avoiding growth assets altogether in favour of cash or low-risk instruments that feel “safe” but quietly erode purchasing power over time.
2. Recency Bias
We extrapolate from recent experience. If markets have risen strongly for two years, it feels natural to expect that to continue. If they’ve fallen sharply, the pessimism can feel permanent. Recency bias is one reason investors often enter markets at or near peaks and exit at or near troughs — exactly the opposite of what a rational long-term strategy would prescribe. The decade after the global financial crisis, when equity markets delivered exceptional returns, was also the period during which many South African retail investors remained underexposed to growth assets.
3. Herd Mentality
The impulse to follow what others are doing is deeply embedded. In investing, this drives capital into whatever asset class or sector is currently generating the most conversation — crypto in 2021, AI-linked stocks in 2023 and 2024, local property in the years before interest rates rose sharply. The narrative always feels compelling at the time. The entry prices rarely do, in retrospect. Herd mentality also works in reverse: widespread capitulation during a downturn often signals the best opportunities for those who can stay objective.
4. Confirmation Bias
Investors tend to seek out information that confirms what they already believe, and discount information that challenges it. If you believe markets are overvalued, you’ll find plenty of evidence to support that view — and ignore the data suggesting otherwise. Confirmation bias makes it difficult to update your outlook when the facts change, and it can lead to sustained under-allocation to assets that are, in fact, performing well.
5. Overconfidence
Most investors — and most people — overestimate their own skill and knowledge relative to the average. In investing, this manifests as excessive trading, concentrated positions, DIY portfolio management without adequate diversification, and a reluctance to seek professional advice. Overconfidence tends to peak after a period of strong returns, which is precisely when it is most dangerous.
6. The Endowment Effect
We place a higher value on things we already own than on equivalent things we don’t. In investing, this often appears as an unwillingness to sell underperforming assets — not because the fundamentals support holding, but because selling means acknowledging a mistake. Investors sometimes hold legacy policies, underperforming RAs, or concentrated single-stock positions long past the point where a rational assessment would suggest restructuring — simply because they have owned them for a long time.
| Bias | What It Looks Like | Typical Cost |
|---|---|---|
| Loss Aversion | Avoiding growth assets; holding losing positions too long | Inflation erosion; missed recovery gains |
| Recency Bias | Chasing last year’s best performer; panic in downturns | Buying high, selling low — the classic return gap |
| Herd Mentality | Investing in trends at peak valuations | Concentrated exposure to inflated assets |
| Confirmation Bias | Staying out of markets; refusing to update a thesis | Persistent under-allocation to growth |
| Overconfidence | Excessive trading; inadequate diversification | Transaction costs, tax drag, concentration risk |
| Endowment Effect | Holding legacy products past their usefulness | Opportunity cost; suboptimal portfolio structure |
What to Do About It
Recognising a bias is necessary but not sufficient. The research is fairly clear that awareness alone doesn’t reliably prevent the behaviour — partly because biases operate below the level of conscious reasoning, and partly because each biased decision feels entirely rational in the moment. What actually works is structure: building decision-making processes that reduce the opportunity for emotion to intervene.
Invest with a clear purpose. The most effective anchor against emotional decision-making is a plan that articulates what the portfolio is for — not just in general terms (“I want growth”) but specifically: what income is needed, when, and from what sources. Investors with a clear destination are better positioned to evaluate short-term market movements in context. A 15% drawdown in a portfolio you don’t need to draw from for ten years is a different proposition from the same drawdown in a portfolio you’re drawing from today.
Automate where possible. Regular, automated contributions to a retirement annuity, unit trust, or offshore wrapper remove the discretionary decision from the equation. You don’t have to decide whether now is a good time to invest — you invest regardless, which means you capture downturns as well as rallies.
Follow a rules-based framework. A pre-agreed rebalancing schedule, target asset allocation, and drawdown rate are worth far more than the ability to make clever in-the-moment calls. Rules constrain behaviour in ways that good intentions alone do not.
Limit exposure to financial noise. Daily market commentary, short-term performance tables, and social media are structurally designed to generate reaction. For a long-term investor, most of what they communicate is irrelevant and some of it is actively harmful. Understanding the difference between volatility and permanent loss of capital is more useful than monitoring daily price movements.
The Role of a Financial Advisor in Behavioural Coaching
One of the clearest arguments for working with a financial advisor — particularly a fee-only advisor with no incentive to trade — is not fund selection or tax optimisation. It’s having someone whose job it is to keep you from making expensive decisions under stress.
During a sharp market correction, an advisor can do something you cannot easily do for yourself: show you the data, hold the context, and provide a calm counterpoint to the anxiety you’re feeling. That function doesn’t require special insight into what markets will do next. It requires the ability to distinguish between a situation that demands action and one that demands patience — and to communicate that distinction clearly when it matters most.
The JP Morgan research, referenced above, suggests this behavioural coaching function alone is worth more than the advisory fee in most years. That’s not a sales argument. It’s an observation about the mechanics of compounding: losing 3.5% annually to poor decisions costs more, over time, than almost any fee structure.
For a broader view of what financial planning actually entails, see our financial planning guide. For those approaching or in retirement, where the stakes of poor decisions are particularly high, working with an advisor who understands the decumulation phase can make a material difference to outcomes.
Frequently Asked Questions
What is the behaviour gap in investing?
The behaviour gap is the difference between the return a fund delivers and the return its average investor actually receives. JP Morgan research consistently estimates this gap at around 3 to 4 percent per year, caused by poorly timed decisions — selling during downturns, buying near peaks, or switching funds after a period of underperformance. Over twenty years, this gap can reduce end wealth by almost half.
What is loss aversion and why does it matter for investors?
Loss aversion is the tendency to feel the pain of a financial loss more acutely than the pleasure of an equivalent gain. Research suggests losses feel approximately twice as powerful psychologically. This causes investors to hold losing positions too long, avoid growth assets that feel risky, and sell during market downturns at exactly the point when staying invested would serve them best.
How do cognitive biases actually affect investment returns?
Biases influence the timing and nature of investment decisions in ways that consistently reduce returns. Recency bias leads investors to buy high and sell low. Herd mentality drives capital into assets near peak valuations. Overconfidence produces excessive trading and inadequate diversification. Each decision feels rational in the moment, which is part of what makes these biases so persistent and costly.
Can understanding behavioural finance make me a better investor?
Awareness helps, but structure matters more. Investors who understand their biases are better equipped to question their instincts, but research suggests that awareness alone doesn't reliably prevent emotional decisions. What works is building a rules-based investment process — clear objectives, a target allocation, automated contributions, and a rebalancing discipline — that reduces the opportunity for emotion to override strategy.
What is the role of a financial advisor in managing investor behaviour?
Beyond fund selection and tax structuring, a good advisor provides a behavioural anchor — someone who can hold context during volatile periods and prevent costly decisions made under stress. Fee-only advisors, who have no incentive to trade, are particularly well-placed to fulfil this role. The value of that function is significant: JP Morgan research suggests the average investor loses around 3.5% annually to poor behavioural decisions alone.
Behaviour Is the Biggest Variable
The technical side of investing — asset allocation, fund selection, tax efficiency, offshore structuring — matters. But research consistently shows that behaviour matters more. An investor with a mediocre portfolio and excellent discipline will, over a long enough time horizon, outperform an investor with an excellent portfolio and poor discipline.
That’s not a reason to be passive about investment quality. It’s a reason to take the behavioural dimension seriously — to understand your own blind spots, build structures that constrain impulsive decisions, and be honest about the conditions under which you are most likely to make costly mistakes. For most people, those conditions are periods of market stress, when the emotional pull to act is strongest and the consequences of acting are most severe.
The good news is that these patterns are well-documented and, to a meaningful degree, manageable. Having a clear plan, a rules-based investment process, and access to objective professional guidance doesn’t eliminate the emotional dimension of investing. But it does reduce its power to determine outcomes.
If market volatility is making you question your investment strategy — or if you’ve never had a clear framework to fall back on when things get uncomfortable — we’re happy to talk it through. It’s a practical conversation, not a sales pitch. More on the kinds of clients we work with, here.
This article is for informational purposes only and does not constitute financial advice. Henceforward (Pty) Limited is an authorised representative of Graviton Wealth Management (FSP 8772). References to market events and historical performance are for illustrative purposes only and are not indicative of future results. Projections and illustrations are for discussion purposes only. Consult a qualified financial advisor before making any investment decisions.