When that day comes, and it will, you are not to shed a tear for Jimmy Carter.

Cry for Rosalynn and their 69 years together. Weep for his family, his state, or his country. But don’t let a single tear drop for the former president himself. Because there is nothing to mourn.

Over nearly 91 years, Carter has squeezed every drop of juice from the orange he’s been given. That was the subtext of his extraordinary, 38-minute press conference at the Carter Center on Thursday to announce that four cancerous lesions had been found on his brain.

Metaphors crowd into an event like this, each screaming for attention: Jimmy Carter as an elderly Tom Sawyer, dictating the terms of his own memorial service. Jimmy Carter as the high-stepping trumpeter and lead celebrant in his own New Orleans-style jazz funeral.

The one we’ll go with is Jimmy Carter the marathon runner, giddy and relieved at having crossed a finish line – upright, and of sound mind if faltering body.

Unless you’ve actually accompanied a spouse, parent or grandparent through the last stages of decline, you can’t truly grasp the personal victory that unfolded off Freedom Parkway in Atlanta three days ago.

At 10 a.m. sharp, the door opened and out came the former president with an unfaltering gait, led by a Secret Service contingent that is now 39 years old – older than most of you reading this.

Down three steps without hesitation or assistance. Carter wore a blazer and, most appropriately, a pair of faded blue jeans. People forget that it was the peanut farmer, not Ronald Reagan, who introduced denim and Willie Nelson to the White House.

Journalism has an informal maxim. Whenever the health of a president – serving or former – is discussed, assume that a great deal of fibbing is taking place. The examples are many: Franklin Roosevelt and his heart disease, John F. Kennedy and his Addison’s disease, Ronald Reagan and his battle with Alzheimer’s.

Carter will now be cited as the rare exception that proves the rule. He described his melanoma in wincing detail. First there was his liver.

“The tumor was 2.5 cubic centimeters. They removed about 85 cubic centimeters. Which is about a tenth of my liver,” he began. And then on to the four spots on his brain.

“They are very small spots, about two millimeters - if you can envision what a millimeter is. I’ll get the first radiation treatment for melanoma in my brain this afternoon,” Carter said.

He then described, with some bemusement, the mask that he had been fitted with the day before at Emory University hospital. It would be used to immobilize his head later that afternoon, as he received that dose of radiation.

What was his first reaction upon learning that the cancer had spread to his thinking unit? “I was pleasantly surprised that I didn’t go into an attitude of despair or anger or anything like that. I was just completely at ease,” the former president said.

That Jimmy Carter had summoned the detachment of a former nuclear engineer was obvious. Separating oneself from the emotion of the moment is an excellent tool for managing the tsunamis that life sends your way. And no tsunami rises larger than life’s end.

But detachment and mastery of detail are also signs of a man in full control of his life and the organization that orbits him. After his brief introductory remarks, Carter played a game of Twenty-one Questions with reporters, some of whom were barely a third of his age.

Again, he wielded details. Yes, he was still hoping to make a Habitat for Humanity trip to Nepal. “It would require an airplane flight from Kathmandu to the Chitwan area, which is south down toward the Indian border,” he said. Turn left at the third elephant on the right, he might have added.

He spoke of Israel and Plains and his Baptist faith.

And yes, Carter had regrets. He should have sent one more helicopter to rescue those hostages in Iran. He would have been re-elected.

Many news outlets reported the deliberately humble thing he said next: “But that may have interfered with the foundation of the Carter Center. If I had to choose between four more years and the Carter Center, I think I would chose the Carter Center.”

What most didn’t report is that Jimmy Carter the politician is still with us. The former president paused for half beat, and then added: “Could have been both.” That was his true regret.

Much has been said about Carter redefining the nature of the post-presidency. But in fact, we may not understand how high the 39th president has set the bar. For most of us, even ex-presidents, lucidity at 90 – much less relevance – is the most we can hope for.

As an ex-president, Carter has been a hard act to follow. Former President George H.W. Bush – just a few months older than Carter — jumps out of airplanes and is mentally active, his friends say. But a form of Parkinson’s disease prevents him from walking. He no longer addresses the public.

Former presidents Bill Clinton and George W. Bush are younger and healthy, but their post-president activities are restricted by a spouse and brother, respectively, seeking the White House.

It is not just about being active. It is being successful in that activity. Four years after he left the White House, Theodore Roosevelt, perhaps America’s most athletic president, joined an expedition into the Amazon basin that darn near killed him.

Carter plunged into the wilds of Africa. And likely will be the first ex-president given credit for eradicating a disease – the loathsome Guinea worm disease, or dracunculiasis. Erasing it from the earth is at the bottom of one of the largest bucket lists in U.S. history.

“I’d like the last Guinea worm to die before I do,” Carter said – again summoning the details. “I think right now we have 11 cases. We started out with 3.6 million cases. I think we have two cases in south Sudan and one case in Ethiopia and one case in Mali and seven cases in Chad. That’s all the Guinea worms in the world. And we know where all of them are.”

That was Question No. 20. There was one more, and then a 90-year-old gentleman in a blazer and blue jeans rose, climbed unassisted the three stairs out of the auditorium, and left with his wife and family.

In its own way, you could classify that exit as something close to a miracle. You and I won’t live to see another one like it.