An Uncharted Road
In December 2020, Tesla joined the S&P 500. The stock surged nearly 70% in the five weeks leading up to inclusion – not because the company’s fundamentals changed, but because index funds had to buy roughly $80 billion worth of Tesla shares regardless of price. ¹
This wasn’t investors analyzing Tesla’s value. It was algorithms following rules: “Stock enters index. We buy stock. End of analysis.”
Welcome to the unintended consequences of the index revolution.
Noble Beginnings
Jack Bogle launched the first index fund in 1976 with a simple insight: most active managers can’t beat the market after fees, so why pay them? The logic was perfect – low costs, tax efficiency, and broad diversification.
For decades, that model worked beautifully. But when passive investing overtook active management in 2019, ² the balance began to shift. Today, index funds and ETFs account for over 50% of U.S. equity market assets. ³
In investing, however, dominance leads to distortion.
The Mechanical Market
When rules-based investing drives market volume, new dynamics emerge:
The Automatic Buy Problem
Index funds don’t ask, “What’s this company worth?” They ask, “Is it in the index?” When a stock enters the S&P 500, passive funds must buy – creating what researchers call the “index inclusion premium.”
Tesla’s surge before joining wasn’t based on analysis. Studies show stocks typically jump 5–10% upon inclusion, then often give back those gains within a year. ⁴ It’s mechanical buying divorced from fundamentals.
The Correlation Shift
In 2000, the average correlation between S&P 500 stocks was around 0.30 – stocks moved somewhat independently. By 2025, that number exceeds 0.70.⁵
Translation: everything moves together. Individual performance matters less; market-wide flows dominate. When everyone owns the same 500 names, they all become one trade – and that can lead to mispricing.
A Modern Example
In March 2024, Zions Bancorporation (ZION) was removed from the S&P 500 and added to the S&P MidCap 400. Nothing was “wrong” with the bank; its market cap simply dipped below the large-cap threshold. Index funds sold automatically because they had to.
The price fell for three months, bottoming near $39. But fundamentals told a different story – revenue growth, earnings up 13.5%, strong loan portfolio. By October 2025, the stock recovered to about $57 – a 45% rebound. The business didn’t change; passive flows did.
A Symbiotic System
What many investors overlook is how dependent passive investing is on active traders for price discovery.
Price discovery – the process by which markets agree on fair value – relies on analysts, institutional research, and active buying and selling. Index funds, by contrast, are price takers. They follow prices set by others, adjusting weights mechanically.
That’s fine while enough active participants exist. But when their share shrinks too much, market efficiency suffers. It’s like everyone following GPS instead of learning to drive – it works perfectly until the map runs out of roads.
Opportunity in the Chaos
We’re not suggesting anyone abandon indexing. For investors who prefer simplicity or low costs, index funds remain excellent vehicles for diversification. But when passive flows become dominant enough to distort pricing, active managers gain an advantage.
This isn’t fearmongering – it’s capitalism. One business’s constraint becomes another’s opportunity. As passive investing grows, it naturally opens pockets of inefficiency that active investors can exploit. That’s the self-correcting mechanism that keeps markets healthy.
Every Auction Needs Many Bidders
At its core, the market is an auction of opinions. The broader the spectrum, the more efficient prices become. When too many participants act mechanically, pricing gaps widen – creating the openings that fundamental and quantitative investors can fill.
At LUL Wealth Management, we merge fundamental analysis (what’s actually valuable?) with quantitative signals (what’s temporarily mispriced?). Where index funds ask, “What should we own?”, we ask, “What’s worth owning right now?”
By identifying distortions created by passive flows and rebalancing quarterly, we seek opportunities likely to correct over the next three to six months. It’s not magic – it’s the market doing what it’s always done when one force grows too dominant: creating room for the opposite to thrive.
Active Opportunities Ahead
The indexing revolution delivered tremendous benefits – lower costs, broader access, better diversification. But its very success surfaced new structural challenges.
As passive dominance weakens traditional price discovery, new inefficiencies emerge. Firms able to identify and profit from these pricing distortions responsibly will find the next wave of active opportunity – one that rewards research, and independent thinking.
So, how much of your portfolio is passively managed? Do you see opportunities emerging in actively managed small and mid-caps?
IMPORTANT DISCLOSURES:
This article is for educational purposes only and does not constitute investment advice. Past performance does not guarantee future results. All investing involves risk, including potential loss of principal.
The views expressed regarding passive vs. active investing represent analysis of market structures and are not predictions of future market performance. Both passive and active strategies have risks and potential benefits that vary by individual circumstance.
Index funds and passive strategies have provided strong returns for millions of investors and continue to be appropriate for many portfolios. This article explores structural market changes, not blanket recommendations.
LUL Wealth Management is a registered investment advisor. The strategies discussed reflect our current thinking but may not be suitable for all investors. Consult with a qualified financial advisor before making investment decisions.
References:
¹ CNBC, “Tesla’s addition to the S&P 500 could be one of the largest rebalances in history” (December 2020)
² Morningstar, “A Landmark Year: Passive Equity Funds Attract More Than Active for the First Time” (2019)
³ Investment Company Institute, “2024 Investment Company Fact Book”
⁴ Chen, Noronha & Singal, “Index Changes and Losses to Index Fund Investors,” Financial Analysts Journal (2006)
⁵ Research Affiliates, “The Remarkable Rebound in Stock Correlations” (2023)