I have a modest suggestion about character motivations that might perhaps seem out of place on this list.
Rather than the usual "I want to invent the biggest CrIg spell ever," or "I shall become an archmagus" or "I shall learn the secrets of the Fay" or "I will be the greatest Quaesitor ever" or "I shall create a giant steel golem" or "I will break a rule of magic," how about setting aside a character's magical abilities and affiliations for a bit, then consider his motivations, and then consider his magic as a means toward an end, rather than an end in and of itself? The magic might still become part of motivation, but characters are most interesting when they are people first and story elements second.
Motivation consists of four elements:
a) What do I want?
b) Why do I want it?
c) How far will I go to get it?
d) What aids me and hinders me in my quest?
The object of desire seems to be the most important element of motivation, but really it is the least. It is only a McGuffin, kind of the way the forces of evil can build a Death Star or create a Killer Virus or some other Big Thing the Good Guys Must Destroy.
No, it is the why that drives motivation, the second question that is by far the most important, because even if the object of desire is attained, the character's inner nature drives him onward.
And it is the third question that describes the intesity of intent that further describes the character and gives him depth. Consider a prince who wants to kill his older brother to gain the throne. The throne is (a) the object of desire. His willingness to kill his older brother is (c) the length to which the prince will go to achieve his aim. This length is also more important that the actual object of desire. Who cares if it's a throne or a shrub? He's going to kill his brother for it!
But without knowing why he is willing or eager to kill his brother for the throne, we still don't understand the prince's motivation.
Let's consider some whys. He wants the throne because he believes the kingdom needs a competent king. Or because he believes his brother is a diabolist. Or because he has always hated his older brother, who has always made life miserable for him. Or because his wife has put him up to it.
Ah! Now things are interesting. Motivation has nothing to do with a throne or even killing, but with duty or vengeance or envy or need to please someone else.
The last factor of motivation is necessary, because without it no action is possible. If a character lacks any ability to attempt to further his aims - nothing happens. If nothing hinders a character in his quest, then we have a very boring game, if the game in any way centers around this character.
To summarize, motivation is simply "I want A because of B and I'll go so far as C to get it, using and being opposed by D."
So don't neglect those magi who fall in love, or who want to support their mundane families, or who have a rivalry with a peer. This is the heart of motivation and character, not spells or swords or potions or theory.
The game isn't about magic, it's about people.
