Wrong button, dork

She's finally stopped rubbing herself. "You can touch things with your mind, and you choose to touch a button? Not my button?"

"I've never tried to move a small part of something big ... I mean people-sized before."

"Nice save. Why not try?"

"The last time I tried something new, all of this happened. And unless you're hiding a dozen girls in the next room I'm not about to take any risks."

"So do a small test. And for honest-to-god magic I can find you a dozen girls."

You spot an envelope. Pointing, you ask "Can you think of anything potentially difficult I'm overlooking about moving the flap of an envelope?"

"Nothing at all. You've stopped, thought about it, asked someone who is not an expert in any way. Let's do this."

The envelope opens and closes itself repeatedly. You bring it over to inspect, still laying on your back.

"Now try tearing it."

You do, and you freeze. That was a bit more energy than the button earlier, but there is a perfect slice. No rough edges. Precision slicing like the sharpest blade ever created.

"Well, I'm never using that on a person."
"Why not?"
"It's got perfectly sharp edges. Great for cutting and scraping, but not for a gentle caress. And it didn't give any sign to me what was about to happen. I think it'd cut just about anything and then just use the energy. The entire system is like buying things on your credit card without ever seeing the price tag."

"Are you the ultimate assassin now? Damn that's hot."

My roommate has issues.

"Yeah I .. wait, no. That feels wrong. Hmm... why could that be wrong? Those gut feelings have been totally correct so far, and seem to be part of the power."

"Is it something about humans?"

"I think so. Maybe... yes! Any being with inherent magical potential also defends itself from direct magical damage. So I could try to cut off someone's head but I'd sort of ... slip around it."