ERISA's prudence standard is written in one sentence and litigated in thousands of cases. This article explains what the duty actually requires of the people who sit on a retirement plan committee, and why the Supreme Court's short unanimous opinion in Hughes v. Northwestern University did more damage to the defense bar than its brevity suggested. It traces the standard from the statutory text through Tibble v. Edison and its continuing duty to monitor, explains why offering a menu that includes cheap options does not excuse leaving expensive ones on it, and walks the anatomy of the excessive-fee complaint including share classes, revenue sharing, recordkeeping benchmarking, and proprietary funds. It then covers what changed after Cunningham v. Cornell made prohibited-transaction claims dramatically easier to plead, the standing problem Thole created for defined benefit participants, the actual-knowledge rule of Intel v. Sulyma that gutted the three-year limitations defense, and the newest litigation waves over forfeitures and cybersecurity. It closes with what a defensible process looks like in practice, because prudence under ERISA is a procedural standard and the file is the defense.