Wizards in Arunia are strange creatures. I mean, I'm sure they're strange everywhere, but the inspiration for Arunian wizards comes from a pastiche of particularly strange sources. Of course there's some Gandalf in them, but there's a whole lot of Soulcatcher and Lady in there as well. What, never read the Black Company? You should! Whether or not you should before we go on with this little essay is up to you.
Magic is a powerful force, and those few who wield it are substantially different from the masses of Artless Arunians... even if it is only because they think they are. Sorcerers and wizards hold themselves apart from society, as evinced by the infamous Arunian phrase "Wizards build tower." Schools of like-minded wizards have existed (generally in the far past) and continue to exist (in some exotic lands) but they have the deck stacked against them from the outset.
Men (and elves) are contentious creatures. They cannot be in each other's company for long without coming to a disagreement over something. Competing philosophies lead to bloodshed but it needn't be something so high-flung as that: theft, envy, greed, insanity... there's a whole host of ills just waiting to insert themselves into social situations and put people at odds. There are destined to be arguments, even if they are only small ones that end with every party agreeing they were in the wrong, collectively taking the blame, and moving on.
Except wizards aren't like most people. When your neighbor gets angry that you've emptied your chamber-pot on his store-sign, he yells at you because that's what he can do. If he's very angry he might threaten you with a club or bit of wood. That's because your neighbor can't bend the fabric of reality to his will. Wizards are, after all, self-important little demigods. And like demigods of any real-world religion, they're prone to infighting.
The nature of the kind of personalities generally produced by magical training means they are, for the most part, far from humble. After all, they can cause the world to rearrange itself in a more pleasing manner just by speaking a few words. That kind of power can go to a fella's head. These aren't your average folk any longer but rather a group of intelligentsia prone to dramatics and hysterics. When a wizard is wronged, things can escalate very quickly. If the argument is between two wizards, then you had better run for the hills because they can turn the countryside into a little patch of hell with their fighting.
I didn't say schools don't exist though, did I? Oh, they do. There are magi who can put aside their massive egos for long enough to band together and make a single cult-like cabal. These wizards generally take an Us vs. Them attitude and for the most part have intricate social conventions to prevent the sorts of cataclysmic conflict I was describing above.
But more than all this, wizards are anti-scholars. Scholarship, by its nature, is research and understanding that one strives to make available to the world. No scholar worth his salt would want to come to a great revelation and then keep it to himself. That would be madness! The entire point of their career is to share what they've learned and, in some small way, perhaps better mankind.
Such is not the case with a wizard. Knowledge among magi is literally power, and for a paranoid group of mortal gods it can be deadly to give your opponents access to the same knowledge (power) that you have. Wizards guard their advances against all comers save their apprentices, and even then they may be cagey. Within schools, spells and knowledge are shared freely... but Gods help you if you betray your school by teaching any of those tricks to an outsider.
Mercenary, is what wizards are, and they may trade spells for money with other mages... but only if they don't feel threatened by them. Powerful wizards make bank off of their less powerful kin who are still in training... but they certainly don't sell their prized counterspell to someone just as mighty as they are. That would be like selling a thief the keys to your house!
So, wizards are lonely and they trust very few. They rarely have lasting romantic relationships for this very reason. The power differential between a mage and a normal person does not instill respect—the sorceress who takes a farmer to her bed may have occasion to remind him that she is a mighty wizard and he a mere tiller of earth. However, relationships between two wizards are strained for the opposite reason: the other might turn on you in a moment of anger or passion and therefore is not to be trusted.
Thus, most magi in Arunia have but one person they can rely on, truly: their apprentice. This paternal relationship ensures that their knowledge and brand of magic does not pass out of the world with them when (if) they perish. Apprentices are nearly never biologically children of their master (for the reasons stated above: few magi have children) which makes this a sort of adoptive parenthood.
You know what they say: Wizards are subtle and quick to anger.