Hey guys, this is my first forum post.
The way I see it, spells increase the probability of something happening. If we follow the multiverse theory (which I strongly believe in), then it is possible not to just alter your luck, but matter itself.
The multiverse theory states that for every action from a being with a consciousness, creates an infinite number of other universes in which the being made a different decision, thus letting things turn out far more different. Spells (in my opinion) are tools that guide you along the universes (I don't know exactly how, though). Thereby, you could go into a universe using spells where, let's say, you become a werewolf.
If you have a different theory, then please reply.