Again contemplating the differences between the games and the writing. In particular backstory.
Indeed, RPG characters get away with leaving a lot of questions open. Do sorcerers have their powers manifest spontaneously? Or does someone have to notice their potential and teach them how to cast the spells? (A DM would have to consider that the first would limit the ability to multiclass into it -- which may be wise.) Do clerics and paladins have to be ordained, and if so, what connection does that give them to the ordaining church? In my Gamelit world, there are secular clerics and paladins: a scholar at a university might be a cleric of the knowledge domain, and as time goes on between the novels, it grows more and more likely that any given magistrate will be a paladin. But those are jobs. The question of true, freelance clerics and paladins -- well, there are always the cults, but adhering to them has problems of its own.
Sometimes, in true sword & sorcery style, you can write a novel about a character whose background doesn't matter, generally the professional adventurer who finds ordinary life dull, but you can't count on it.