John C. Bogle

That message is simple: Gross return in the financial markets, minus the costs of financial intermediation, equals the net return actually delivered to investors. Whether markets are efficient or inefficient, investors as a group must fall short of the market return by precisely the amount of the aggregate costs they incur. It is the central fact of investing.

Investors have learned, and learned the hard way, that in mutual funds it's not that "you get what you pay for." It's that, almost tautologically, "you get what you don't pay for."