I know it is not a very plausible answer but if physics tell us everything can be, and magic falls upon that category, then magic is an explanation for any behavior or phenomena.
That is the same reason why, when someone says "I have a huge exam tomorrow morning, how can I stay awake all night?" or "I need to be in two places at the same time, what can I do?" I answer "with magic". Sure, I know that the most likely responses to, say, the first question would be "coffee", "sugar", "amphetamines", or "remind yourself that your life depends on you passing this exam", as for the second question would be "just go to the most important event" or, in any case, "submit yourself to a clonation procedure". Still, I think that magic is just a good enough way to stay awake or to duplicate yourself in order to achieve satisfaction upon any of those two tasks.
Yes, for you to use magic to stay awake, to appear on two places at the same time, to conjure up some climatic conditions, or to kill or save a certain race, you need, first of all, to have supernatural powers and to be able to tap and alter the situation you are up against to. But it is not my concern if you do, indeed, have powers or, in case you do, if you know how to use them. You were just posing a question and I was just providing an answer.
And that is why, when on a dark, moonless night, I am coming up to my car in an almost empty underground parking lot, keys in hand, and a serial killer jumps out of nowhere and starts stabbing me violently in the ribs, as I lay on the cold cement, choking on my own blood, I will think "Yup, I told you so. You made some crazy witch or warlock angry, and this is why this is happening to you."