While total market index funds are the gold standard for most, they are theoretically sub-optimal for anyone who isn't perfectly average.
The Myth of the Universal Portfolio
Low-cost total market index funds are the most sensible investment for the vast majority of people. The advice to simply "own the market" is robust, yet it lacks the nuance required for sophisticated asset allocation. To understand why, we must look at the evolution of financial theory. In the 1950s, Harry Markowitz developed Modern Portfolio Theory, suggesting that investors seek to maximize returns for a given level of variance. This led to the Capital Asset Pricing Model (CAPM), which posits that in an efficient market, the market portfolio is the most efficient possible allocation for every investor. If we stop there, market-cap-weighted index funds are the undisputed finish line of investing.
However, the CAPM is an imperfect reflection of reality because investors do not care about portfolio variance in a vacuum. They care about how their investments interact with the rest of their lives. Robert Merton’s Inter-temporal CAPM (ICAPM) expanded this by acknowledging that investors are concerned with how their portfolios co-vary with their labor income, the price of goods, and future opportunities. In this light, the market portfolio is no longer the single optimal choice for everyone; instead, it is the 'multi-factor efficient' portfolio—the average of what everyone else is doing.
The Risk of Being Average
The market portfolio is optimal for the average investor, but almost no one is perfectly average. If your life circumstances make you more or less sensitive to economic risks than the median person, a total market index might actually be sub-optimal for you. For example, if you are a tenured professor with high job security and little sensitivity to market cycles, you have a higher capacity to endure specific risks that the average investor avoids. Conversely, a business owner whose primary income is highly correlated with the stock market might need a portfolio that looks very different from the index to hedge against a total wipeout during a recession.
This creates a theoretical opening for those willing to deviate. If you are not exposed to common risks outside of your portfolio—such as a retiree with stable fixed income—or if you are simply willing to stomach more volatility than the average person, you can tilt your portfolio toward assets that offer higher expected returns. These assets are priced higher because the 'average' investor finds them too painful to hold during bad times.
The Value Premium as a Risk Hedge
The most prominent example of this deviation is the 'value' tilt. Research by Fama and French suggests that small-cap and low-priced value stocks provide returns that the broader market cannot explain. These stocks are often under financial distress, carry high leverage, and face significant uncertainty. They are riskier than growth stocks in bad economic times and only slightly less risky in good ones. Because they deliver poor returns exactly when labor income and consumption tend to fall, most investors demand a premium to hold them.
If you choose to tilt toward value stocks, you are essentially volunteering to take on the risks that the average investor is trying to hedge against. You are trading the comfort of the market index for a higher expected return, fueled by the fact that you can survive the 'state of the world' that scares others. This is not a free lunch; it is a calculated decision to be the person who holds the assets no one else wants when the economy turns sour.
The Practical Costs of Departure
While the theory supports deviating from the market, the practical implementation is fraught with challenges. The first is the risk of misinformation. When you buy the total market, you are effectively hedging against your own ignorance. You accept the market price as fair. The moment you tilt toward specific factors, you are making a bet. Each time you trade to maintain that tilt, you may be trading against a skilled active manager who possesses better information than you do.
Furthermore, being different from the market introduces significant monitoring costs. A total market ETF is a 'set it and forget it' instrument. In contrast, a factor-tilted portfolio requires constant oversight to ensure the portfolio is still delivering the intended exposures efficiently. You have to endure periods where the market is booming while your specific tilt is lagging, which creates a psychological burden that many investors are unprepared to carry.
Who Should Stay the Course?
Ultimately, the decision to avoid total market index funds depends on two factors: your unique risk profile and your temperament. If you are a skeptic who wants to minimize the risk of trading on bad information, or if you simply do not want to spend your life monitoring factor exposures, the total market index remains the gold standard. It is a highly efficient way to capture the returns of the capitalism without needing to outsmart the collective wisdom of the crowd.
However, for those who understand that the market is merely an average of everyone else's fears and needs, there is a path to higher expected returns. If you have a stable career, a long time horizon, and the stomach to be different when being different feels wrong, tilting away from the market portfolio is theoretically the more optimal choice. The market index is a safe harbor, but for the investor with a unique capacity for risk, it may be a harbor that leaves too much potential on the shore.