I think writing fantasy is difficult. When creating a new world with new rules (i.e. magic, physics, politics), authors have to remain consistent. The magic in Harry Potter is a great example. J.K. Rowling establishes different economic classes in the wizardry populace. For example, the Weasley family is considered poor. But the Malfoys are rich. Very rich.
We see this when Harry goes to the bank and sees his vault open to a pile of gold coins. We see this again in Harry and Ron's first train ride to Hogwarts when the candy cart comes. Weasley frowns and holds up his lunch(?) wrapped in Saran Wrap. But Harry makes it rain with gold coins and buys 'the whole lot'.
Then we see something curious. In the Great Hall after the new students have been sorted into their houses, plates of food miraculously appear out of thin air onto the tables. Ron dives in and gorges himself. This suggests that food, or anything else, can be created out of nothing, which contradicts the idea of economic class. Why does money exist if a basic need like food can be conjured from nothing?
Rowling even acknowledged that she had run into a storytelling problem, and covered herself by showing that house elves prepare the food, and magic is used to teleport the plates of sustenance to the tables. To be honest, I didn't even see the problem until I started to learn the rules of world building.
Now, reading other writers' works, I've had to take notice if/when they're breaking their own rules. But writing about human insecurities is a little difficult. One of the authors in my writing group has a story about a guy who is self-conscious about feeling old. But there are moments where that character feels youthful and moments when he feels old. We've all harped on this fact, that his character seems to flip flop on his own perception of age. That the character needs to be consistent, otherwise the author may lose the readers' trust. The author states that his character's feelings on age depends on the situation.
And that makes perfect sense.
Character traits are defined as something that changes their view of the world. Put it simply, if the character is a man, his view is going to be vastly different than a woman's. A man isn't going to fear rape every time he goes on a first date. But a woman may because she's the physically weaker sex.
Or if a character is narcissistic, then she will see the world as beneath her, or her above it, as seen in the character Cat Grant in Supergirl.
So what we, as fellow writers, are harping on is the consistency of the character trait. But what we did not see is that declaring yourself old or young is not the trait the author intended. The trait is the insecurity of being old. And the character's flip flopping supports that trait. Because if the trait was that he feels old, isn't worth anything because he's old, then flip flopping wouldn't make sense. And it wouldn't make for an interesting story.