The illusion of diversification: How different investments can carry the same risks
Why portfolio overlap, changing correlations, and product structure deserve a closer look.
There is a particular reassurance in looking at a portfolio and seeing variety. Several funds, companies from different sectors, perhaps some bonds alongside equities: the spread itself suggests that care has been taken. Often it has. But a portfolio can look considered while remaining dependent on a surprisingly narrow set of conditions.
This is where diversification becomes more demanding than its familiar definition suggests. Owning different assets is a starting point. Understanding why they might rise or fall together, and how much capital depends on those shared influences, is the work that gives the idea substance. Without that understanding, adding another holding can deepen an existing exposure while creating the impression that it has been reduced.
Consider the investor who holds a broad US equity fund, adds a technology fund and then buys shares in a chipmaker whose prospects they admire. Each decision may have a reasonable explanation. Taken together, however, those decisions may leave more of the portfolio dependent on continued enthusiasm for artificial intelligence than the investor intended.
When different holdings share the same risk
The S&P 500 makes this distinction particularly relevant. At the end of August 2026, its ten largest constituents accounted for 37.8% of the index, with Nvidia, Apple and Microsoft heading the list, according to S&P Dow Jones Indices. A tracker still provides exposure to hundreds of companies, but its performance is influenced disproportionately by a small group. Adding a fund that owns many of the same businesses can reinforce that influence.
There is nothing inherently mistaken about holding a strong view on technology. The difficulty begins when conviction is mistaken for diversification. A portfolio assembled through several products can still express one dominant view about the future, leaving its owner less room for disappointment than the number of holdings suggests.
Why market relationships need revisiting
Even where exposures are meaningfully different, their relationship is conditional. Stocks and bonds provide a useful reminder. In 2022, inflation and sharp interest-rate increases hurt both markets. Morningstar measured a correlation of 0.66 between its US Total Market and US Core Bond indexes that year. From the beginning of 2025 through the midpoint of 2026, that figure fell to 0.11, indicating a much weaker relationship between their returns.
Higher interest rates can reduce existing bond prices while weighing on the value investors assign to future corporate earnings. Under those conditions, two assets held for different purposes can respond to the same pressure. When the economic backdrop changes, their behaviour relative to each other can change with it.
It would be a mistake to treat either period as a permanent verdict. Bonds did not cease to have a diversification role because they fell alongside equities in 2022. Nor does a subsequent low correlation establish how they will behave during the next sell-off. Historical relationships are useful precisely when their limits are understood: they describe how particular assets behaved under particular conditions.
What an ETF label cannot tell you
The same care is needed with the products through which exposure is held. An exchange-traded fund may contain hundreds of securities, or it may offer leveraged exposure to a single company. The familiarity of the format can make that distinction easy to overlook. Yet the diversification associated with a broad fund does not carry over simply because another product uses the same three-letter abbreviation.
Research published by The Compound Insights with Direxion and Vanda found that active retail traders accounted for about 90% of leveraged-fund turnover in its April–July 2025 analysis. A leveraged single-stock fund concentrates exposure in one business and amplifies it. If the product resets daily, its stated multiple applies only to that day’s performance. Over longer periods, compounding can cause returns to differ substantially from the underlying stock’s return multiplied by that same multiple.
For brokers such as FXTM, educational content should help readers understand what an instrument may add to, or concentrate within, their existing exposure, including costs, leverage and product structure.
Keeping diversification under review
There is also a behavioural challenge. Concentration can develop without a new purchase, as a successful holding grows into a larger share of the portfolio. Reviewing that change requires some distance from the satisfaction of having been right. Strong performance may support the original thesis while leaving more capital dependent on its continuation than was originally intended.
Regular review creates space for that judgement. It does not require constant adjustment, which brings costs of its own, or a response to every market headline. It requires checking whether the relationships behind the portfolio still hold and whether the resulting exposure remains appropriate to the capital at risk.
Diversification offers no assurance against loss. Its purpose is to reduce dependence on any single outcome, and that purpose needs attention as markets and portfolios evolve. A collection of assets can be bought once. The judgement that makes them work together has to be renewed.
Risk warning and disclosures
This article is for informational and educational purposes only. It does not constitute investment advice or a personal recommendation, and it does not solicit any trade. Trading involves risk of loss of capital. Trading Forex and CFDs is high risk and may not be suitable for all investors, and some instruments, including commodities and oil, are especially volatile. Past performance does not guarantee future results. Full Terms and Conditions apply.
About FXTM
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