A flashbulb memory from the archives of my life: It is the summer of 1997, and we are moving my disabled sister, Wendy, into a care home. She is in her bedroom in my parents’ house. She is a woman in her 30s who requires 24-hour care, and my aging parents can no longer provide it. Her life is being dismantled around her — her ornaments gingerly packed away for transport, the cords of her precious stereo unplugged and set aside in a snake-like tangle. My sister cannot understand what is happening. She looks up at me from the floor where she is sitting and shouts angrily: “Why? Why do things have to change?”

This memory keeps coming back to me in recent weeks — ever since the U.S. presidential debate. Superficially, nothing about Wendy would remind us of President Biden’s life story — she never had a chance to play politics or run a country — but the more I see Biden caught in the gears of time, or doing his best not to face it, the more I realize he’s fighting in the same war my sister waged for decades. We are all eventually called up to those front lines, where we all, eventually, lose.

Wendy had a brain tumor when she was a child. Surgery to remove that tumor was fraught with post-operative complications. And yet she defied many odds, living until the age of 52, and regaining mental and physical faculties that doctors initially said had been permanently destroyed. In so many ways, she was the beating heart of our family. I always had the sense that her life told the story of the kind of people we were. She was the person who defied the odds, and we were the ones who never stopped betting on her. It’s a good story. A Hollywood story, even.

At some point, “beating the odds” stories can turn tragic, beginning in microscopic ways. The line between hope and delusion thins, and in the moment, sometimes it is difficult to know when you or your family are crossing it. Some people will never walk again. Some brains will never heal. You also can’t beat odds that are unequivocal. Those aren’t even “odds,” really, because the hoped-for outcome isn’t possible. One of my toughest jobs as a doctor is helping patients and their families face the moment when those odds are ushering them toward an inevitable truth, one we are all tempted to resist.

Like my sister, Biden survived a dangerous neurosurgery, in his case after aneurysms in 1988. But the far more important commonality between my sister and the U.S. president is a personal narrative about overcoming adversity, which Biden alluded to in his widely panned interview with George Stephanopoulos. Biden may be the author of his own narrative of triumph, but in my sister’s case, that story came from the people who loved her. Both were cast in that classic Hollywood role: the fighter you could never count out, no matter the odds.

Practicing medicine has had a way of keeping me grounded when it comes to the notion of “fighters.” While personal characteristics such as resilience do matter, they can’t outpace the inevitable. Decline, and death, are nonnegotiable parts of life.

And yet, there were still times when even I believed that my sister would prevail against any odds. In those early years, every time she almost died, she did appear to bounce back. But it was also true that as the years went on, with each new medical challenge, she was like a basketball with a little less air in it. She no longer bounced. Deflated, she slowly began to disappear. Her brain, vulnerable after surgery and subsequent seizures, had no reserve to mop up new injuries. If she had nine lives, then she also suffered enough for nine lifetimes. By the time she died, she was a husk of her former self.

Biden, too, seems deflated, a husk of the scrappy, inspiring career politician he once was. His seeming lack of insight into the public’s concern for his health is an alarming symptom on its own. Nothing seems to pierce his insistence that he’ll bounce back.

The irony, of course, is that Biden’s self-image as a fighter has served him well until now. He bounced back before, grinned and persevered. His family has likely come to believe in his stature as a “fighter” as a kind of unassailable, mythic truth, and I am sure that story has given them power and comfort during some very hard times. Don’t count Dad out. Other people have made that mistake before.

But “other people” are not the only ones capable of mistakes in judgment when it comes to our loved ones. Some research shows that cognitive impairment in older patients may not be noticed by families unless it is accompanied by behavioral symptoms and signs. Even when someone is struggling with a simple act such as making toast, our long record of confidence in their powers can blind us to what is happening in real time. Even when not just the toaster but the whole house has caught on fire, for families who have seen their loved one pull back from the brink time and time again, it is hard for them to believe they won’t see that same magic trick once more, just in the nick of time.

Time. Isn’t that what it all boils down to? Not so much the nick of time as time’s nicks: death by a thousand little cuts. The story of our lives cannot rewrite the story of life. Things have to change. Sometimes we cannot understand why, and it hurts. But we can’t change the reality of what comes next.

Jillian Horton is a writer and physician. Her first book, “We Are All Perfectly Fine: A Memoir of Love, Medicine and Healing,” is being adapted for television. @jillianhortonMD