@TNT261
A huge part of writing fiction (not set in our world) is making and adhering to rules and mythos you create. Not doing that is bad writing.
I disagree. It's generally bad writing, but it doesn't mean you can't make exceptions.
In this case, the rules we know are the rules Zeff knows. (Actually less than that, we discover his knowledge of magic as he uses it, so there might be more he knows but we don't, yet.)
So there is room to introduce rules that he doesn't.
It's different, for example, from a story that establishes something from an objective or absolute point of view. (actual demonstration from someone, exposition text, literal word of god, etc.)
Showing someone repeatedly shooting fireballs, only to later have that same character mention that you can't start a forest fire with magic would be inconsistent.
On the other hand, having a character mention that you can't make fire with magic, to have another character later shoot fireballs does work. That helps underline the lack of knowledge of the first character as opposed to the second. Which is basically what happens in this chapter. On a much larger scale.
Rule breaking is only bad writing when it is established by the author himself in a definite way. Not when characters do the rule exposition.
That said, it is a delicate trick to use. It is easy to do something wrong when breaking a supposedly established rule.
This case is very touchy because of the concept of subjective time used here: the mage was
not supposed to
actually spend years in confinement, it was only supposed to
feel like it.
Grain saying that it's enough to accumulate years of knowledge and experience is a fragile excuse directed - in part at least - to the reader. Although I do consider it valid, I can understand that not everyone will accept it.