Ooo, ooo, I've got some in-canon theories!
In the beginning of my comic, Adi, one of my two main characters, is unable to use the local form of magic, known as the Song. And there are a lot of community theories as to why that is.
For context, the Song is divine magic given as a gift from the local gods, and as long as one tries to live in a state of harmony with both the forest and the community, everyone from age 12 up is able to learn it. The Song has many words and even whole verses, which do everything from healing, to tracking, to lighting fires, to accomplishing daily tasks. The entire community relies on it heavily for survival in the forest environment where they live. People fall in and out of being able to use the Song if they're feuding with a neighbor or abusing the forest's resources... but once they sort out their issues, they always get their Song back.
Adi has never had it. The gods denied her the Song at age 12 when she engaged in the Song ceremony for the first time, and further efforts to learn it got her absolutely nowhere. This was a MASSIVE SCANDAL. As happens in a small town, everyone knows everyone, and theories starting flying fast and hard.
Theory 1. Adi, in spite of being a 12 year old, must be harboring some fervent loathing of a neighbor. (Except, no one could think of anyone she disliked, especially that hard.)
Theory 2. Adi must've done something that the community would find unforgiveable. (Except no one, including Adi, could think of anything she could possibly have done that would warrant a total denial of the Song!)
Theory 3. Lacking any evidence to wrongdoing on Adi's part, people started speculating that her birth parents (Adi's adopted) must've done something so bad that the gods denied her on principle... even though she's never met her birth parents.
There are probably other fringe theories, but these are the big three-- and they're all wrong.
As you might imagine, though, being the town weirdo that everyone secretly suspects of wrongdoing sort of makes Adi long for adventure... or at least getting out of that town.