The Intelligent Allocator: diversification's 'free lunch' still needs a cook

Why hold a multi-asset portfolio rather than simply owning an index, bonds, or any other investment vehicle that has most recently delivered the best returns? The answer is diversification. The familiar word conceals the effort needed to make it work. A portfolio remains truly diversified only as long as its holdings keep behaving differently from one another and offering different advantages. Maintaining that diversification is a process.

The research is well established. In 1952, Harry Markowitz showed that a portfolio's risk depends not only on the risk of its individual holdings, but also on how those holdings move relative to one another. Combining assets that do not rise and fall in lockstep lowers the portfolio’s overall risk, while its expected return remains simply the weighted average of its components. That insight earned Prof. Markowitz a shared Nobel Prize in Economics in 1990.

A portfolio remains truly diversified only as long as its holdings keep behaving differently from one another and offering different advantages

The investment practice is more nuanced. When Prof. Markowitz had to allocate his own retirement contributions, he did not use the mathematical framework that would later make him famous. Decades later, he explained that he had imagined two possible investment regrets: missing a soaring market or suffering a severe decline while fully invested. Therefore, he initially split his contributions equally between stocks and bonds, creating a portfolio that he could live with. After all, the effects of compounding only reward those who remain invested through difficult periods, and the portfolio that survives is often not the one that looks best on paper, but the one its owner can hold through adversity.

Diversification is often described as the only ‘free lunch’ in investing because it allows investors to reduce portfolio risk without necessarily reducing expected return. But the returns are not free of effort.

What diversification really buys

What role does diversification play in portfolios? We should remember that diversification offers a better investment journey, not necessarily a better end result. In other words, diversification aims to cushion drawdowns, enable faster recoveries, and shield against the only loss that an investor’s patience cannot repair: a permanent impairment of capital.

Diversification aims to cushion drawdowns, enable faster recoveries, and shield against the only loss that an investor’s patience cannot repair: a permanent impairment of capital

In general, higher portfolio returns require higher risk. It’s true that a handful of skilled hedge fund managers have occasionally provided bond-like drawdowns and equity-like returns, but over more than two decades, individual asset classes or markets, on average, have not.

A balanced portfolio does not escape this risk-reward trade-off. Rather, it sits close to the efficient frontier.¹ No single asset class offers higher returns with a smaller drawdown, while the portfolio itself remains dependent on no single asset class or market in isolation.

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The importance of limiting losses is often underestimated. A portfolio that falls 50% must subsequently rise 100% just to break even. But years spent recovering losses are also years missed in compounding returns. The returns of a balanced portfolio compare favourably with the longest recovery period experienced by almost every asset class following a drawdown.

The humbling task of the allocator

All this, however, is based on history. The intelligent allocator cannot know the outcome in advance, and instead must take real-time decisions. That responsibility has three components:

First, we must set out assumptions. Each year we formulate our capital market assumptions (CMAs) to build an expected return and a plausible downside scenario for every asset class, based on prevailing conditions in growth, inflation, monetary policy, and valuations. These are not forecasts of next year's winners but estimates of the compensation investors are likely to receive for bearing different risks. They anchor strategic asset allocation (SAA) decisions and help define what a reasonable, or underwhelming, year might look like before it arrives.

Second, we monitor the two dominant risks. Most of the damage to a balanced portfolio can be traced to two macroeconomic risks: recession and inflation. Over more than twenty years, the only significant and prolonged shortfalls relative to cash and inflation – the minimum return a portfolio should deliver – occurred during the 2008 great financial crisis and the inflation shock of 2022. The recession in 2020 was so brief that rolling 12-month measures barely captured it.

Most of the damage to a balanced portfolio can be traced to two macroeconomic risks: recession and inflation

Over the full period, however, a balanced portfolio outperformed cash in 79% of rolling twelve-month periods and inflation in 77%, exceeding them by an average of 5.4% and 4.8%, respectively, an argument for being invested, and staying there.

The objective of adjusting the asset allocation is not to sidestep every bout of volatility. It is to identify when one of these two major risks is becoming more prominent and position the portfolio accordingly, accepting that such decisions will sometimes prove early and occasionally unnecessary.

The third task is to ensure that a portfolio stays well diversified. Diversification depends on the relationships between assets, and those relationships evolve in economic and market cycles. The most important is the correlation between stocks and bonds. This relationship has shifted regime twice over the past four decades: it was predominantly positive during the 1980s and 1990s, negative during the following 20 years, and positive again since 2021.

The period of negative correlation from 2001 to 2020 conditioned a generation of investors to expect bonds to rise when equities fell. But in historical terms, that period was an exception. That is because when growth is investors’ primary concern, bonds tend to cushion equity losses. When inflation becomes the dominant risk and central banks tighten monetary policy in response, both asset classes may decline simultaneously. That is what happened in 2022, one of the worst years for a USD-denominated balanced portfolio in decades. The lesson for allocators is that diversification never depends on a single relationship or tool, and so portfolios need multiple sources of diversification, along with a disciplined rebalancing process, to be effective.

Concentration can emerge in less obvious ways as well. A portfolio may appear diversified across asset classes even when they all reflect the same underlying theme. Today, one such example is artificial intelligence. Just three chipmaking companies represent more than a quarter of the emerging-market equity index, and the sector is also a dominant weight in the US and some Japanese indices. In addition, hyperscalers account for an increasing share of credit issuance and private financing demand, while copper prices are also becoming influenced by the same AI-infrastructure build-out.

An investor can therefore believe that they are diversified by holding a technology stock, some bonds, a private-credit vehicle, and exposure to industrial metals. Yet all these positions may ultimately be driven by the same underlying AI narrative. The objective is not to avoid the theme but to understand how much of the portfolio depends on it and to choose that level of exposure deliberately.

A portfolio may appear diversified across asset classes even when they all reflect the same underlying theme. Today, one such example is artificial intelligence

The value of an allocator

Strategic asset allocation, and multi-asset investing more broadly, remains valuable because diversification provides a smoother path, shallower drawdowns, and faster recoveries that allow for stronger compounding. Yet diversification is neither permanent nor self-sustaining. It depends on relationships that evolve over time, and some of its most important benefits can disappear precisely when they are needed most, as bond allocations did in 2022.

For this reason, the key question is not why take a multi-asset approach but why an asset allocator matters. In short, because the underlying assumptions must be continuously challenged, risks monitored, new opportunities pursued and a portfolio’s diversification preserved.

Diversification may indeed be the only free lunch in investing, but sustaining it requires constant work. The value of an allocator, therefore, is in combining the ingredients thoughtfully, rebalancing the mix as conditions change, and continually questioning whether a portfolio is truly diversified. Exceptional ingredients do not create a great meal on their own.