That’s a strong defense of individual investors’ decisions to invest in index funds. But that excess performance is only possible if active managers are trading

That’s a strong defense of individual investors’ decisions to invest in index funds. But that excess performance is only possible if active managers are trading stocks. At some point, someone has to decide that one company is a buy and another company is a sell—if we all invested solely in index funds, share prices would move in lockstep (disregarding liquidity). Its a self-correcting scenario. If that were truly the case, then people would start to trade actively, since trading actively would be an easy way to "beat the market".