Passive Investing and Tragedy of the Commons: What if Market Efficiency is Already Melting Away?

Active managers are discretionary traders, who seek mispriced stocks they believe will add excess returns to their funds. Passive investors are non-discretionary traders, they notionally need not worry about valuation, they believe the market is efficient, and thus perfectly reflects all known information. Their investment strategy is largely irresponsive to the price of the asset. Shiller explained, “Indexing …is free-riding on other people’s work” – in other words, active managers. At what point does there become too many passive players, such that they render the market unmoored from efficiency and thus turn the overall market inefficient?