Now, I don't know the rules for Spirit of the Century, so lacking that as a background I might be a little confused, but here's my problem: It seems to me that so long as a wizard does not enter into pacts (such as swearing on his power), it's entirely possible for him (or her) to achieve quite a lot of power and retain free will.  Yet from what I've read, as your PC wizard gains power he will eventually lose free will.  That doesn't quite make sense to me; a wizard, constantly practicing his art and performing it in combat will keep on getting better.  Sure, he might become paranoid and jaded, but I don't see how that will actually override his capability to make decisions.

I understand that creatures like vampires and the Fair Folk are "slaves to their nature", but I think wizards and practitioners aren't comparable if they don't use black magic or enter into demonic pacts and the like.  So maybe I could get a bit of clarification?