The Investor’s Hidden Risk: Behavioural Bias

Investors spend considerable time measuring portfolio risk through volatility, duration, credit spreads and currency exposure. One of the most important risks is harder to quantify: the way investors and their advisers make decisions.

Even experienced investors can be influenced by emotions, personal beliefs and past experiences. They may hold on to a losing investment too long, become overly attached to a successful holding, or take on more risk after a period of strong returns. These decisions are rarely seen on a risk report, but they can have a lasting impact on portfolio performance.

Traditional finance assumes that investors assess information rationally and make decisions in their best interests. In reality, people often rely on mental shortcuts when faced with uncertainty or complex choices. In investing, these shortcuts can lead to costly mistakes. Behavioural finance helps explain why this happens and how a disciplined investment process can help us manage this challenge.

Two Kinds of Bias

Behavioural biases generally fall into two broad categories: cognitive errors and emotional biases.

Cognitive errors arise from the way we process information. Investors may focus on evidence that supports an existing view, misinterpret new information or place too much weight on past experience. Better analysis, structured decision-making and independent advice can help challenge these assumptions.

Emotional biases are harder to address because they stem from feelings such as fear, regret, pride, and attachment. Knowing that a bias exists does not necessarily prevent it from influencing a decision. The aim is therefore not to eliminate emotion, but to recognise where it can interfere with sound investment judgement and put safeguards in place.

Common Biases:

Confirmation bias

Investors naturally look for information that supports what they already believe. Once they become convinced that a company or investment is attractive, they may give positive news more weight than negative developments. Over time, this can lead to an oversized position and a reluctance to reconsider the original investment case.

Anchoring

The price an investor paid for an asset, or the high it reached in the past, can become a reference point for future decisions. An investor may refuse to sell below the purchase price, even when the underlying outlook has deteriorated. But the market does not know what an investor paid, and yesterday’s price is not necessarily a guide to tomorrow’s value.

Mental accounting

Money is often treated differently depending on where it comes from. An inheritance, bonus or investment gain may feel less important to protect than savings built up over many years. This can encourage investors to take risks they would otherwise avoid. Looking at each investment in isolation can also obscure how the assets work together, or against one another, across the overall portfolio.

Loss aversion

For many investors, the pain of losing money outweighs the pleasure of making an equivalent gain. This can lead to two familiar mistakes: holding losing investments in the hope of recovering the original cost, while selling successful investments too early to secure a profit. Neither decision necessarily reflects the investment’s future prospects.

Overconfidence

A run of successful investments can leave investors believing they have more forecasting ability than they actually do. Trading becomes more frequent, portfolios become concentrated and risks receive less attention. Strong market conditions can also make it difficult to distinguish investment skill from favourable circumstances.

Endowment and status quo bias

People tend to value assets they already own and often prefer to leave existing arrangements unchanged. This can be particularly evident with inherited investments or a substantial holding in a family business. Even when a portfolio becomes unbalanced, the familiarity of existing positions can make change uncomfortable. Doing nothing may feel safer, but it still has consequences.

From Individual Decisions to Market Behaviour

These biases do not stop at the individual portfolio level. When many investors react similarly, their behaviour can influence entire markets.

Investors who assume that recent performance will continue may push popular assets higher, reinforcing momentum. Overconfidence, herd behaviour and fear of missing out can contribute to speculative bubbles. When conditions turn, the same tendency to follow the crowd can accelerate selling, while investors who are slow to reassess their assumptions may hold on for too long.

Market movements are not driven by behavioural biases alone, but these patterns can amplify both rallies and downturns.

Building Better Investment Habits

No investor is entirely immune to behavioural bias. The goal is to build a process that makes poor decisions less likely, especially when markets are volatile or emotions run high.

• Look at the whole portfolio. Bring investments across accounts together to understand the true allocation, concentration risks and how different assets interact.
• Reassess investments objectively. Ask, “Would I buy this investment today at its current price?” This helps separate the original investment rationale from the desire to avoid admitting a loss.
• Challenge your own assumptions. Before making a significant investment decision, consider the strongest argument against it. Independent perspectives can reveal risks that are easy to overlook.
• Keep a record of decisions. Document why an investment was made, what could change the original thesis and what would prompt a sale. Reviewing these notes later can help distinguish sound decisions from hindsight-driven outcomes.
• Stick to an agreed investment framework. A clear strategic allocation, supported by defined limits for tactical changes and portfolio rebalancing, helps prevent short-term market movements from dictating long-term decisions.

Discipline Matters Most When Markets Are Difficult

Understanding markets is only part of successful investing. Investors must also understand their own reactions to uncertainty, losses and success.

A well-constructed portfolio can still disappoint if decisions are made due to fear, overconfidence or attachment to the past. Recognising these tendencies and putting sensible disciplines in place helps investors and their advisers stay focused on long-term objectives when short-term pressures make that difficult.