WASHINGTON — A 23-year-old bank robber named Shon R. Hopwood stood before a federal judge in Lincoln, Neb. He asked for leniency, vowing to change.

Judge Richard G. Kopf had no patience for promises. “We’ll know in about 13 years if you mean what you say,” he said. It was 1999.

Judge Kopf reflected on the exchange this month. “When I sent him to prison, I would have bet the farm and all the animals that Hopwood would fail miserably as a productive citizen when he finally got out of prison,” he wrote on his blog. “My gut told me that Hopwood was a punk — all mouth, and very little else.”

“My viscera was wrong,” Judge Kopf went on. “Hopwood proves that my sentencing instincts suck.”

Judge Kopf had just heard the news that Mr. Hopwood, now a law student, had won a glittering distinction: a clerkship for a judge on the United States Court of Appeals for the District of Columbia Circuit, which is generally considered the second most important court in the nation, after the Supreme Court.