Dan Lefkovitz, index strategist at Morningstar, opens with a disarmingly frank admission1: that telling investors to diversify their portfolios often lands with the same enthusiasm as telling them to eat their vegetables. He concedes that giants of the craft have pushed back. Peter Lynch called it "diworsification." Warren Buffett said, "Diversification is protection against ignorance. It makes little sense if you know what you are doing."
Lefkovitz's response is neither defensive nor dismissive. He invokes Harry Markowitz instead: "Diversification is the only free lunch in investing." Then he makes his case, methodically, with index data. So far in 2026, investors who spread their bets across complementary assets have been rewarded in not one but four distinct ways.
Bonds Are Doing Their Job Again
The Morningstar US Core Bond Index carries slightly negative returns year-to-date. Inflation is running hot. Rates are staying higher for longer. By most headline measures, 2026 has not been a banner year for fixed income.
But that misses the point. Lefkovitz observes that when the Morningstar US Total Market Index has declined this year, whether on artificial intelligence sentiment shifts or the outbreak of the Iran war, bonds have "either gained or suffered far milder losses." They have earned their reputation, in his words, as "ballast," significantly reducing portfolio volatility even in a difficult rate environment.
This is not a one-year story. From the start of 2025 through the midpoint of 2026, the correlation coefficient between US stocks and US bonds stands at just 0.11, barely positive. In 2022, that same figure was 0.66. When both stocks and bonds collapsed together that year, the death of diversification was declared. The data since then says otherwise. As Lefkovitz notes plainly, "correlations change."
Geography Has Mattered
International equities have outperformed US stocks through the first half of 2026. That outperformance narrowed after late February, when the Iran war sent energy prices spiking, but the margin has held. And this follows a strong 2025 for international stocks as well, aided by US dollar depreciation and a rally in European banks and defense. The net result is that US investors with global exposure have profited meaningfully over the past 19 months.
The cynical read is not lost on Lefkovitz. He acknowledges that international stocks trailed US equities dramatically for the 15 years between 2010 and 2024, and that part of recent outperformance traces to emerging-market semiconductor companies, which offer limited diversification benefit to investors already heavy in US tech. But the broader ex-US universe remains structurally different from the US market. It is far less top-heavy, far less concentrated in technology, and financial services, at 22%, is its largest sector. Lefkovitz frames this as an opportunity set argument: "geographic leadership has historically gone in cycles," and the global universe contains companies and growth trends that domestic-only allocations simply cannot access.
Small Caps Found Their Moment
US small-cap stocks have endured years of underperformance. The last calendar year they meaningfully outperformed large caps was 2016. For most of the period since, they have lagged even when macro conditions appeared favorable.
In 2026, the picture has changed. Lefkovitz cites his Morningstar colleague Susan Dziubinski: "Small-cap stocks are having a moment, a pretty big moment." Attribution analysis on the Morningstar US Small Cap Index points to contributors including smaller AI names like Sandisk and Bloom Energy, as well as healthcare companies like Revolution Medicines. But the broader diversification thesis also holds: small caps are less top-heavy, less tech-heavy, cheaper on a price-to-earnings basis, and industrials, not technology, is their largest sector grouping.
Niche Diversifiers Are Earning Their Place
Beyond the core building blocks, Lefkovitz surveys what else has worked. The Morningstar MLP Composite Index of midstream energy stocks has delivered superb returns, aided by rising energy prices from the Iran war. This echoes a pattern worth remembering: natural resources-related investments often rise during inflationary periods. They were, as Lefkovitz notes, "practically the only bright spot in 2022, when stocks and bonds both sank." REITs, through the Morningstar US REIT Index, are also having a strong year, aided in part by data center buildouts.
At the same time, Lefkovitz is measured about complexity. He cites a colleague's work noting that alternative investment strategies have faced a difficult stretch, and that private equity and private credit do not necessarily offer significant diversification benefits. His colleague Amy Arnott puts it cleanly: when it comes to diversification, "more isn't always better."
5 Key Takeaways for Advisors and Investors
1 Bonds still work as ballast. Despite negative total returns, fixed income has meaningfully reduced portfolio volatility in 2026. The stock-bond correlation has returned to near-zero from the extreme readings of 2022. The death of diversification was a premature declaration.
2 Correlations are not permanent. The shift from a 0.66 stock-bond correlation in 2022 to 0.11 from 2025 through mid-2026 is a reminder that structural relationships between asset classes evolve. Portfolios built for only one correlation regime carry hidden risk.
3 International exposure has earned its keep. After 15 years of underperformance relative to US equities, international stocks have outperformed for 19 consecutive months. Geographic diversification broadens the opportunity set and reduces dependence on a single market's trajectory.
4 Small caps reward patience. After years of lagging, US small caps are contributing in 2026. Their structural differences, lower tech concentration, lower valuations, and broader sector exposure, make them a genuine complement to large-cap growth holdings.
5 Simplicity holds the advantage. A few well-chosen, complementary asset classes, stocks, bonds, international equity, and selective real asset exposure, go a long way. Complexity through alternatives and private markets does not automatically translate into diversification benefit.
Footnote:
Lefkovitz, Dan. "4 Ways Portfolio Diversification Has Paid Off in 2026." Morningstar Indexes, 3 Aug. 2026, indexes.morningstar.com/insights/perspective/bltf09c31e6e0dbdcc9/4-ways-portfolio-diversification-has-paid-off-in-2026.
