Moral of the story, short version: YOLO.
Moral of the story, long Marquise version: Doctors' misdiagnoses, when they don't get you killed, are motivational.
This is one of those books you judge by the ending, and that's what I'm going to focus on. But first, I have to say that the ending doesn't bother me, and my critique is more based on what I believe would have been a better development of the climax rather than the outcome itself. I don't believe the ending ruins the story; at best it makes it a tad too sentimental and too convenient to be realistic.
Going straight to the point, I don't think Valancy not having the disease she thought she had is, in itself, fine. It's the how she came to believe that I am not fine with. I'll explain my reasoning with spoilers ahead.
You see, I think Valancy should've believed that because of a doctor's misdiagnosis, and not because of a doctor's correct diagnosis getting mixed in the mail and sent to her by mistake. That is what I find non-credible and its implausibility stretches credulity. "Oh, the letters were sent to the wrong address and you're healthy now!" How possible or common is that, really? I have never heard of such a case, which isn't to say it has never happened, but if it has, it must be a millions-to-one event.
I have, however, heard numerous cases of doctors' misdiagnoses. I have experienced one myself. When I was a child, I had frequent stomach trouble, and my poor mother took me from one physician to the next until my mid-teens, and all of them told her a different thing. Some gave us ridiculous diagnoses and some gave us more serious diagnoses, but none of them was correct, and I spent years taking all sorts of pills and vitamins to no avail. Until my mother, fed up with all those doctors, took me to the capital's top gastroenterologist, one of the best in the country, which examined me and laughed at everything my mother told him the other docs had told her. My stomach problem was a common issue, he said, not frequent in children but easy to treat, and he derived me to an American colleage that was visiting those days. I got treated, and my stomach has never troubled me again. I have iron guts that can withstand everything, even the spiciest Mexican and Asian food you can throw at me.
Point being, Valancy's heart disease should've been a true misdiagnosis. Dr Trent's mistake should've been in diagnosing her wrongly, not in sending her the letter meant for another patient.
I mean, a diagnosis of a life-threatening condition turns your existence upside down and is deeply traumatising. How many of you know about a relative, a friend, a neighbour, etc., that got a cancer diagnosis, for example? I'm sure many of you have, and thus know how deeply affecting it is. A person that is told they have a lethal condition and not much time left to live is forever changed. Some for the better, some for the worse. Some break down completely and never recover, some go to their grave fighting courageously. Even when it appears to outsiders that the person is the same, they never are. A chronic or fatal illness never leaves you the same on the inside, never.
So, imagine how much more affecting it would be if you were to find out that your doctor screwed it up and told you a lie, be it from human error or incompetence?
What then? What would you do? Surely some of you do also know of cases where a person was misdiagnoses something very serious and somehow survived or beat the odds to live much longer than the doctors predicted. It needn't be a case of misdiagnosis, either, because there's people who will prove the doctors wrong and defeat the odds to live when they were told they wouldn't.
For me, it would've been more realistic and impactful if Valancy had confronted Dr Trent and he had realised and admitted to his misdiagnosis. She already had gone to him thinking he must've been mistaken in his diagnosis, so for him to tell her it was a mail switcheroo didn't sit well with me. Valancy had braved familial condemnation and social ostracism in order to live her last months on this Earth like she wanted, had grabbed the bull by the horns and became independent, finding love in the process, only to learn that it was a problem with the letters?
No, it takes away the emotional impact of her fatal disease as a motivator to improve her lot in life to die happy. Imagine what it would be like if you were told you had cancer and only 6 months to live, and next you go to the doc, he tells you the diagnosis was for the old bat down the street from you and that you're just a silly healthy chit.
Of course, it would've been even better if Valancy had simply beat the odds and lived longer than the condition allowed. But maybe that would've been even less convincing and more convenient plotline than the mail switcheroo? Probably. And that leaves us with the misdiagnosis as the best outcome.
As I was saying, it didn't bother me to the point of ruining the book, but there's no convincing me it couldn't have been better than what it was.
Another point from the ending that I didn't find convincing was Barney Snaith's backstory. No, I don't mean the famous writer identity but the true identity. That was completely unnecessary, in my opinion. That "poor little rich boy" infodumpy monologue by the end was overkill. He could've kept his mystery writer arc perfectly well, but to add the rest to it was too much for me. I liked Valancy the most and that he treated her kindly and was always thoughtful to her already helped endear him to readers, so he didn't need more sugar heaped on top.
To conclude, I enjoyed this book and had a good time reading it, the imperfect ending didn't overturn that.