The views expressed here are those of the author, the chief investment officer of Robinhood Markets.

By Stephanie Guild

NEW YORK, June 16 (Reuters) - For much of the past four decades, investing in equities seemed pretty simple. Interest rates trended lower, corporate taxes declined and globalization expanded. Those forces lifted valuations broadly, muting the consequences of individual company decisions. You just had to be invested.

That time appears to be over.

The shift began well before last year’s tariff surge or the proliferation of AI. Four structural tailwinds that powered asset values for a generation have weakened or reversed — and the investment industry has been slow to acknowledge this.

FOUR TAILWINDS FADE

The first was continuously declining interest rates. The 10-year U.S. Treasury yield tells the story: from a peak of nearly 15% in August 1981, rates declined to 0.6% in the summer of 2020 — a 96% drop in the cost of money over roughly 40 years.

That decline became the foundation for higher asset valuations across the board for decades, reducing interest expense as a share of earnings for companies and lifting equity multiples.

Today the U.S. 10-year yield sits in a range of 4.5% to 5%. Given that several disinflationary trends, like globalization, have stalled and price pressures look set to remain elevated from spiking geopolitical tensions and the AI arms race, interest rates are unlikely to repeat that historic descent.

The second tailwind was falling corporate taxes. The U.S. federal corporate rate peaked at 52.8% in 1969, according to the IRS, and fell to a flat statutory rate of 21% under the 2017 Tax Cuts and Jobs Act — the lowest level since the early 20th century.

That steady reduction boosted net margins, allowing companies to be more competitive globally. This trend, in combination with falling borrowing costs, helped lift the U.S. equity market.

In fact, according to a 2023 Federal Reserve paper, 42% of total U.S. corporate profit growth between 1989 and 2019 was attributable to the combined impact of both declining interest expenses and corporate tax rates.

The third was high government debt tolerance. The U.S. debt burden has ballooned in recent decades – both because of escalating spending needs, particularly during the global financial crisis of 2008-09 and the COVID-19 pandemic, and because of falling tax rates.

Total U.S. public debt has grown from roughly $1 trillion, or 31% of GDP, in 1981, to $38.5 trillion, or 122% of GDP, today. Annual interest expense is now projected to exceed $1 trillion this fiscal year, according to the Congressional Budget Office. The CBO also expects U.S. debt-to-GDP to reach approximately 130% by 2036.

That trajectory leaves little room for further tax reductions or other forms of stimulus that could serve as wind at investors' backs.

'PEAK 65'

The fourth tailwind was natural investing demand. Baby Boomers – born between 1946 and 1964 – built their wealth during years when all three of the above supportive trends were at their peaks. They are now estimated to hold half of all U.S. household wealth, according to the Fed.

Much of this is in retirement accounts, with nearly half the $49 trillion in U.S. retirement assets owned by Baby Boomers, according to the Investment Company Institute. These accounts often rely heavily on index funds.

Demographics help explain why that tailwind is fading. That generation is now reaching what demographers call "peak 65". Based on research from the Retirement Income Institute, more than 4 million Americans will turn 65 each year between 2024 and 2027, and by 2030, all Boomers will be 65 or older.

Required minimum distribution rules - which typically kick in at 73 - mean an increasing share of that wealth will be forced out of equity markets. Estimates from various sources put the net equity outflow at $250 billion to $800 billion annually over the coming decade.

CASH COW TO CASH USER

Another reversal is playing out on the corporate side. The largest companies in the S&P 500 spent the past decade returning capital aggressively: the tech sector alone bought back $2.6 trillion of its own shares in that period, according to Yardeni Research and S&P Dow Jones Indices. That era may be over.

Total capital expenditure by the major technology hyperscalers is expected to exceed $1.1 trillion in 2027, according to JPMorgan, as megacap tech firms race to build AI infrastructure. The biggest names in the index have shifted from cash cows to cash users.

For passive investors heavily concentrated in those names, that is a structural change in the return profile of their portfolios.

Benchmarks based on market cap are backward-looking by design - and that’s now a problem. The changes we are witnessing from AI and the other structural shifts are altering the real economy faster than the common benchmarks can evolve.

The consequences for investors are already visible. Intra-stock correlations in the S&P 500 – a measure of how much individual stocks move together – have fallen sharply since 2022, returning to levels not seen since before the GFC.

In recent decades, when rates were near zero and tailwinds were in place, stocks moved broadly in unison. Now, stocks are increasingly diverging based on company-specific fundamentals: capital allocation, balance sheet discipline, and the quality of management decisions. For the first time in a long time, fundamentals truly matter.

ERA OF JUDGMENT

Of course, the picture is not without nuance. Signs of a recession could prompt the Fed to cut rates sharply, restoring some of the valuation support that higher rates have removed. Or AI could boost productivity enough to curb inflation and spur growth, broadly lifting margins and meaningfully reducing the deficit.

And the Trump Accounts initiative — which would see the government make contributions into index funds for children born between 2025 and 2028 — could create a new structural source of demand for passive vehicles that could partially offset Boomer outflows.

But as we stand today, the tailwinds that supported broad-based equity performance in recent decades have fractured.

Passive investing remains a cost-effective foundation for many portfolios. But for the first time in a generation, it may no longer be sufficient on its own. Assessing individual company fundamentals and correlations between firms is now critical for the modern investor.

The past several decades rewarded simplicity. The next phase will reward judgment.

(The opinions expressed here are those of the author, Stephanie Guild, CFA, Chief Investment Officer of Robinhood Markets.)

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