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We have likely all heard the saying, "Don't put all of your eggs in one basket." But if you've been investing over the last decade, it's hard not to wonder: Why not? Is diversification even worth it anymore?

The S&P 500 has been on an incredible run. Driven by companies like Microsoft, Apple, Amazon, Alphabet, Meta, and Nvidia, U.S. large-cap stocks have rewarded investors extremely well. For the 10-year period ending June 30, 2026, the S&P 500 returned approximately 15% annually.

If your portfolio also included international stocks, small-cap companies, or bonds, you may have found yourself wondering whether they were really worth owning. It's a fair question. When one part of the market consistently outperforms, it can be tempting to ask, "Why not just put everything there?"

That's exactly why diversification can feel frustrating at times. It's also exactly why it matters.

What Is Diversification?

Diversification isn't about trying to own everything. It's about recognizing one simple reality: none of us know what the future holds.

Rather than trying to predict which stock, sector, or country will outperform next year, diversification spreads your investments across different parts of the market. The objective of a diversified portfolio isn't to have the best-performing portfolio every year, but rather it is intended to build a portfolio that can hold up across many different market environments.

A diversified portfolio won't always be the top performer. In fact, over the last decade it often wasn't. That doesn't mean diversification is flawed—it simply means one part of the market happened to outperform everything else.

The Risk of Concentration

Looking backward, concentration always seems obvious. Looking forward, it's much harder.

Every generation has its success stories—companies that seemed unstoppable and rewarded investors tremendously. Looking back, it's easy to wish we had owned nothing but those winners. The problem is hindsight is perfect.

For every company that goes on to become the next Microsoft or Amazon, many others never lived up to expectations. According to research from J.P. Morgan Asset Management's study:

• Approximately 40% of companies in the Russell 3000 declined at least 70% from their peak and never fully recovered.
• Roughly two-thirds of individual stocks underperformed the overall index during their lifetime.

You might own the next big winner—but history suggests you're just as likely to own a company that significantly disappoints. Diversification helps reduce that company-specific risk.

Losses Hurt More Than Gains Help

One of the most overlooked concepts in investing is that losses and gains aren't equal.

If an investment falls 50%, it needs to gain 100% just to get back to even.

If an investment falls 75%, it needs to gain 300% to recover.

Large losses become increasingly difficult to overcome. A diversified portfolio won't eliminate market declines, but it may help reduce the impact of concentrating your investments in a single company, sector, or asset class.

Market Leadership Changes

One of the biggest mistakes investors can make is assuming that whatever has worked recently will continue indefinitely.

Over the past decade, U.S. large-cap stocks have significantly outperformed much of the rest of the world. It's understandable why many investors question whether they need exposure to anything else. History tells a different story.

From 2000 through 2009—often called the "Lost Decade"—the S&P 500 produced a negative annualized return. During that same period, areas such as U.S. small-cap value stocks and emerging markets delivered much stronger returns. 

Does that mean those areas will outperform over the next decade? Not necessarily. No one knows what the next decade will look like. That's exactly why diversification exists. Diversification isn't designed for the decade we just experienced. It's designed for the decades we haven't experienced yet.

Rather than trying to predict which asset class will lead next, diversification accepts that market leadership changes over time and keeps your portfolio distributed across multiple areas of the market. The table below shows various asset class returns dating back to 2006.

The Biggest Benefit May Surprise You

One of the greatest benefits of diversification has nothing to do with returns—it may make it easier to stay invested during periods of market volatility.

Investors are emotional. Markets simply reflect that. When portfolios become highly concentrated, the ups and downs can become much larger. Those bigger swings often lead investors to make poor decisions—selling after markets fall or chasing whatever has performed best recently.

A diversified portfolio won't eliminate volatility, but it can make the ride smoother for many investors. And over decades, staying invested is often far more important than trying to pick the next winner.

The Bottom Line

Diversification isn't about maximizing returns every single year. It's about building a portfolio that doesn't rely on one company, one sector, or one country being right.

No investment strategy eliminates risk, and diversified portfolios will still experience difficult years. But historically, market leadership has changed, surprises happen, and yesterday's winners don't always stay on top.

Investing is full of uncertainty. Diversification doesn't eliminate that uncertainty—it acknowledges it by helping ensure your financial plan isn't entirely dependent on a single variable.

Important Disclosures

This material is for informational and educational purposes only and is not intended as individualized investment, tax, or legal advice. Investing involves risk, including the potential loss of principal. Past performance is not indicative of future results. Please consult your own tax advisor, attorney, and/or financial professional regarding your specific circumstances.