Prudence serves as the keystone for the ERISA standard of fiduciary conduct. The rule requires a fiduciary to act with the care, skill, prudence, and diligence under the circumstances then prevailing that a prudent man acting in a like capacity and familiar with such matters would use in the conduct of an enterprise of a like character and with like aims. The language is drawn in part from the common law of trusts, which judges prudence exclusively in terms of the twin objectives of preserving the estate and attaining adequate return.