"[P]lan sponsors and service providers attempt to justify an imprudent investment option by claiming that they are simply complying with the DOL's and the courts' adoption of Modern Portfolio Theory (MPT) as the applicable standard for assessing the prudence of investments.... [But in 2007, the Fourth Circuit drew a] distinction between one person putting together one investment portfolio, who can ensure that the investment options are put together in such a way as to take advantage of MPT's cornerstone principle -- effective diversification by factoring the correlation of returns of the investments chosen -- as opposed to including an otherwise imprudent investment option in a menu of investment options for a defined contribution plan, where the plan participants may, or may not, understand MPT and how to properly design an effectively diversified investment portfolio." [DiFelice v. U.S. Airways, No. 06-1892 (4th Cir. Aug. 1, 2007)]