Is Holding the S&P 500 Really Diversified? Why 10 Stocks Made 72% of This Year's Gains

Does buying the S&P 500 actually diversify you?

No. Today's S&P 500 isn't a fund evenly spread across 500 stocks — it's closer to a concentrated bet on the top 10 names.

Most people think, "I'm safe, I'm in an S&P 500 index fund." You've been told to just buy the index and hold it forever. It sounds smart, it sounds diversified, it sounds safe. But here's what nobody tells you.

What the numbers actually show

The S&P 500 is, by name, 500 stocks — the symbol of diversification, of not putting all your eggs in one basket. Yet right now the top 10 stocks make up roughly 40% of the entire index. And 72% of the S&P 500's gains this year came from those same 10 names.

In other words, when someone says "I'm diversified, I own the S&P 500," what they're really saying is, "72% of the money I made came from just 10 stocks." Which makes you wonder why you own the other 490 — because this year, those 490 did effectively nothing.

The smartest investors have left the index

Mohnish Pabrai — Charlie Munger's close friend and one of the greatest living investors — was asked about the S&P 500 and answered in a single word: "bearish."

His logic is simple. At today's prices, stocks are overvalued. The S&P 500 trades at a price-to-earnings ratio around 30, while the long-term average is 16. That makes stocks roughly twice as expensive as normal — more extreme than in 2000, right before the dot-com crash.

And what is Pabrai doing with his own money? He has zero in the S&P 500 and zero in mega-cap tech. Warren Buffett's Berkshire Hathaway also sold its S&P 500 index fund. The same people who always told everyone to own the index have themselves sold it.

Even the biggest bull is warning

You might think, "Pabrai is a cautious value investor — that's just how those guys talk." So let me bring in someone from the opposite end: Tom Lee, head of research at Fundstrat.

He's the most consistently bullish voice on Wall Street. He called the 2023 rally when everyone else predicted a recession, and he called the 2024 and 2025 rallies too. That perma-bull is now warning of a 20% correction.

His three reasons: First, new Fed leadership is creating uncertainty — markets get nervous when the person controlling interest rates changes. Second, AI valuations are being repriced — the market is starting to realize these stocks may not be worth what we paid. Third, policy fragmentation like trade wars is creating headwinds that could slow profits.

My takeaway

I think both messages point to the same place. It's rare for the most cautious value investor and the most optimistic strategist to flash warning signals at the same time.

The simplest check you can run today: take the total you hold in index funds and multiply it by 0.4. That's how much sits in just 10 stocks. If you have $100,000 in the S&P 500, $40,000 of it is tied to 10 companies. And many people own those same 10 names separately on top of that — sleepwalking into a very concentrated bet without realizing it.

Before you trust the word "diversified," find out what your index is actually betting on.