Josh Strange is the Founder & President of Good Life Financial Advisors of NOVA. The firm works with federal employees and contractors.
Financial advisors and wealth managers often talk about the benefits of diversification. And they should.
When investors have too much exposure to a single asset—or even just a handful—broad-based market declines can cause them to incur massive portfolio losses, potentially sabotaging their financial goals, including retirement. For the most part, this dynamic is well understood.
It’s why millions have historically embraced low-cost, passively managed index funds; they are designed to help investors gain diversity through exposure to a broad range of companies. Yet there’s a storm brewing within such funds that is gathering speed, and when it hits, the fallout could be messy.
Here’s why the next downturn could be especially destructive for many investors, as well as what they can do about it.
Overly Concentrated Indexes
The top 10 stocks in the S&P 500—including Microsoft, Amazon, Meta, Alphabet and Nvidia—account for nearly 40% of the index, making it unusually top-heavy. Valuations across the board are also well above historical averages, reaching levels not seen since the bubbliest periods of the dot-com era.
These dynamics are becoming more pronounced each day. That’s because when millions of workers contribute to their 401(k)s, they direct a huge chunk of those flows into target-date funds, many of which are heavily weighted toward vehicles tracking indexes like the S&P 500.
As those inflows continue, the largest companies get bigger and more valuable. And thanks to the market-cap-weighted structure of most of those funds, their influence will become more outsized.
The Rise Of The Retail Investor
Retail investors have become more influential than ever. According to Vanda, such individuals added $1.3 billion to the market each day through the first six months of 2025, while estimates suggest they now account for up to a third of all trading volume.
As an advisor, I’m conflicted about this trend. I support more people investing. Yet how this group sometimes invests does make me uneasy, as they tend to concentrate on big names that have produced monster returns in recent years (including many of the companies mentioned above, along with more speculative corners of the market). This impulse contributes to indexes becoming increasingly—and perhaps, dangerously—imbalanced.
Behavioral Finance
In theory, it’s possible to argue that high levels of hyper-concentration within indexes and the funds that track them are somewhat immaterial for investors with an eye toward retirement. Thanks to dollar-cost averaging and the tendency of markets to climb over the long term, a setback today will amount to little more than a blip years from now.
This is true, though, only if an investor has patience. Most do not, even if they say they understand the importance of keeping emotions in check. With retail dollars exerting more influence than ever, their behavior could lead to quicker and larger losses than usual for stocks when the next extended period of volatility grips the market.
A skeptic would likely say the caveat to all of this is corporate earnings. They’ve been strong for multiple quarters, and if they continue to beat expectations, all of this is a non-issue.
In that case, the current rally will likely continue, and everyone will be happy. However, that’s the point—it won’t continue forever.
While the adage “bull markets don’t die of old age” is true, all of them do die eventually. It’s why, at the end of the day, diversification is still the best defense investors have. And although that approach may not entirely shield you from the risks of index concentration, retail-driven momentum and human behavior, it will help you weather any investing environment, good or bad.
Tips For Investors
Smart investing begins with knowing exactly what you own and ensuring it aligns with your goals, values and risk tolerance. Take the time to look under the hood. Using tools like Morningstar can help you see what’s inside your funds, where you might be concentrated and whether you’re truly as diversified as you think.
It also helps to stay forward-looking. Don’t just focus on where the market has been. Pay attention to where it may be heading. Look at the size and mix of companies you own, how they’ve tended to hold up in tough markets and how managers are making decisions inside the funds you choose.
You’ll never get diversification perfectly timed, but staying focused and thoughtful will help keep your portfolio strong over the long run.
The information provided here is not investment, tax or financial advice. You should consult with a licensed professional for advice concerning your specific situation.
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