The growing sense that the findings of financial economics implied that one should simply "buy and hold the market" was possibly one reason why economists found the CAPM's "egregious" implication that there was only one optimal portfolio, the entire market, less shocking than Sharpe had feared, helping give him the confidence to abandon his earlier, strained alternative of multiple optimal portfolios. In that respect at least, the emergence of indexing meant that the world of investment practice came closer to that posited by finance theory.

Donald MacKenzie, An Engine, Not a Camera, loc. 385