Most investors are taught a simple rule: when stocks fall, bonds should cushion the loss. And when both become uncertain, gold should provide protection.

But what happens when all three fall at the same time?

That is exactly what we as investors experienced recently.

Brent crude surged to around US$109 per barrel. The US 10-year Treasury yield approached 5%. Equities declined, bond prices fell, and gold ended the week lower despite escalating geopolitical tensions.

This was not simply bad luck. The same force was hitting every asset: inflation.

Higher oil prices raised fears that inflation could return. Bond yields rose, pushing bond prices down. Higher interest rates placed pressure on stock valuations. Even gold struggled because investors could earn close to 5% from interest-paying assets.

So, is diversification no longer working?

Or have investors misunderstood what being diversified really means?

This has already happened this year

The recent decline was not the first time stocks, bonds and gold moved down together.

During the first two weeks of the US–Israel–Iran conflict earlier this year, Brent crude rose by more than 41%. Yet instead of money simply flowing into traditional safe-haven assets:

• The S&P 500 fell 3.5%.
• Developed-market equities fell 8.6%.
• Emerging-market equities fell 8.7%.
• Long-term US Treasuries fell 4.3%.
• Gold fell 3.6%.

The chart tells us an important story.

When oil prices rise because of a supply shock, the market may not see it simply as a geopolitical crisis. Investors may also see higher production costs, renewed inflation and the possibility of further interest-rate increases.

That combination can hurt several asset classes at once.

The opportunity cost of holding every asset has changed

The decline in stocks, bonds and gold may look like three separate problems. In reality, they are connected by one common factor: the rising return available from US Treasuries.

When the US 10-year Treasury yield moves close to 5%, it resets the hurdle rate for almost every other investment.

Treasuries are generally treated as the benchmark “risk-free” asset in global markets. If investors can earn close to 5% without taking corporate or equity risk, every other asset must offer a sufficiently attractive return above that level.

For equities, this additional return is known as the equity risk premium.

Investors accept the uncertainty of company earnings and fluctuating share prices because they expect equities to deliver higher returns than government bonds over time. But when Treasury yields rise, that return gap becomes narrower, especially when stock valuations are already high.

Investors then begin to ask:

“Am I being adequately rewarded for taking equity risk when Treasuries are paying close to 5%?”

If the answer is no, they may sell stocks and move towards government bonds. Stock prices must then fall until their expected future returns become attractive again.

This also explains why the market has remained heavily focused on AI-related stocks.

When the risk-free return is close to 5%, companies offering only modest growth may struggle to attract investors. The market naturally gravitates towards businesses believed to have the greatest potential to grow their earnings and generate returns sufficiently above the Treasury yield.

AI currently offers one of the strongest growth stories in the market. The expansion of AI computing, data centres, cloud platforms, enterprise software and cybersecurity gives selected companies the potential to deliver exceptional earnings growth.

The market is therefore not simply chasing technology. It is searching for assets with enough return potential to clear a much higher hurdle.

However, high potential returns also come with high expectations. If AI companies fail to deliver the earnings growth already reflected in their share prices, their valuations could fall sharply.

The same change in opportunity cost affects gold.

Gold does not generate earnings, pay dividends or distribute interest. Its return depends largely on someone being willing to pay a higher price for it in the future.

When interest rates were close to zero, the cost of holding gold was relatively low because investors were giving up very little income elsewhere.

But when Treasuries yield close to 5%, the holding cost becomes much more visible: investors are forgoing the interest income they could have earned from government bonds. This can place pressure on gold even during periods of geopolitical uncertainty.

Existing bonds are affected as well. A bond paying 3% becomes less attractive when newly issued Treasuries offer close to 5%. Its price must fall to bring its effective return closer to prevailing market rates.

The entire relationship can be summarised as follows:

• Higher oil prices raise inflation concerns
• → inflation concerns push Treasury yields higher
• → higher Treasury yields reduce the appeal of existing bonds and gold while raising the return hurdle for equities
• → investors become more selective and concentrate on sectors such as AI that appear capable of delivering stronger growth.

This is why stocks, bonds and gold can fall together while some AI stocks continue to attract capital.

It is not because traditional assets have suddenly lost their value. It is because the return available from Treasuries has become more competitive, changing how investors judge the potential reward from every other asset.

Correlations do change over time

For much of the period between 2000 and 2020, stocks and government bonds often moved in opposite directions.

Many investors began to assume that this relationship was permanent.

It was not.

Over the five years, the correlation between US Treasuries and the S&P 500 has turned from negative to 0.53. In other words, stocks and bonds had increasingly been moving in the same direction.

The chart above shows us that the negative relationship familiar to today’s investors was more characteristic of the two decades that have passed.

Stock–bond correlation has become positive when uncertainty about inflation becomes more important than uncertainty about economic growth. The logic is quite straightforward:

• Weak economic growth usually hurts stocks but may help bonds as interest rates fall.
• Higher inflation can hurt both stocks and bonds because it may force interest rates higher.

The danger of searching for a bond replacement

When bonds fail to protect a portfolio, the natural response is to search for something to replace them.

But some of the popular alternatives may contain even more stock-market risk. For example, Private Credit funds and Bitcoin became very popular post-COVID. But research shows these alternatives have no better correlation compared to US Treasuries over the past five years:

Source: AQR, using data from Bloomberg, Cliffwater and Cboe, ending February 2026.

The key number here is equity beta, which measures how much stock-market risk may be hidden inside another investment.

Although bonds had become more positively correlated with equities, their equity beta remained much lower than the other alternatives. Replacing bonds blindly with private credit, or Bitcoin, could therefore increase the portfolio’s dependence on equities—the opposite of what you intended.

The lesson is not that these assets are necessarily bad investments.

The lesson is that a different name does not automatically mean a different risk.

So, is diversification broken?

The short answer is No.

But it also means we should stop assuming that bonds will protect a portfolio under every possible market condition.

Diversification does not mean something in your portfolio must rise whenever another investment falls. It also does not mean your portfolio will never experience a loss.

Diversification means your financial future does not depend entirely on one company, one country, one asset class or one economic outcome.

For example, you may own ten different technology funds and believe the portfolio is diversified. But if all ten funds own many of the same companies, they may react almost identically during a market decline.

Another investor may own fewer investments but spread the money across liquidity, income-producing assets and long-term growth assets. The second portfolio may be better diversified because the investments perform different jobs.

Owning more investments does not necessarily mean owning more sources of return.

Diversification matters more during retirement

A younger investor who is still working may have time to wait for markets to recover. They can also continue investing their monthly salary at lower prices.

A retiree faces a different problem.

Daily expenses continue regardless of whether markets are rising or falling.

If too much money is invested for long-term growth, the retiree may be forced to sell stocks, bonds or gold during a downturn to fund living expenses.

This turns a temporary decline into a permanent loss and leaves less capital available for the eventual recovery.

Therefore, retirement diversification should not begin with:

“How many investments do I own?”

It should begin with:

“Where will my income come from if several markets remain weak at the same time?”

A simpler way to structure retirement assets

This is the principle behind my Kueh Lapis Retirement™ Framework.

Instead of placing all your retirement money into one portfolio, your assets are organised into three layers:

• Guaranteed Income for essential expenses
• Variable Income for your desired lifestyle
• Bonus Income for long-term growth and additional spending

Each layer has a different job. This reduces the risk of having to sell long-term investments simply because markets are temporarily down.

Stocks, bonds, and gold falling together can make diversification feel useless.

But diversification was never a promise that something in your portfolio would always be making money.

Its real purpose is to stop one market event from permanently damaging your financial future.

The recent market decline is a reminder that asset relationships can change. Bonds will not always rise when stocks fall. Gold will not always protect you during a crisis. And owning more funds does not necessarily make a portfolio safer.

True diversification is not about making sure something always goes up.

It is about making sure your retirement plan can keep going when several things go down.

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