This is a minor thing that bugs me: When people point out some inconsistencies or other kind of unrealistic details or events in a work of fiction, sometimes someone will say something along the lines of "this is a movie about magical unicorns and wizards and magic, and you complain that the main character can fly?" Extremely rarely, if ever, is this argument valid.
If we take that arbitrary example, it's not a question of the main character being able to fly. It's about the internal consistency of the universe set up by the work of fiction, and willing suspension of disbelief.
A work of fiction, no matter how fantastical, is well-written when it describes and depicts a world with consistent and plausible rules, which the work follows. It doesn't really matter if some of these rules do not follow the real world, as long as they are well-established, consistent, plausible and not changed or broken at a whim.
It's a sign of bad writing when such internal rules are changed or broken arbitrarily, especially if it's done to suddenly resolve some otherwise unsolvable situation. (In other words, this is especially bad if it's used as a deus ex machina.) For instance, if the work of fiction depicts the protagonist as a human, has not established in any way that humans can fly, or that the protagonist can do so, and flying humans do not even otherwise make any sense even within this fictional universe, and then in the third act the protagonist, out of nowhere, just can fly to save the day, for no apparent reason other than the author suddenly deciding so, this breaks willing suspension of disbelief and is unrealistic within this context (even if there were otherwise fantastical elements to the story.)
This is often a sign of lazy writing. Either the author couldn't bother to come up with a more realistic solution, or couldn't bother to go back and change previous parts of the work to establish this in a plausible manner. (In some cases it can be clearly seen that the author did go back to previous parts and inserted this fact here and there, but it was clearly an afterthought, artificially tacked onto the story just so that it could be used later. If this is obvious, it isn't much better.)