Everyone has part of them that needs to be reined in. It’s that little urge you sometimes feel to hop over the edge of a great height, when you’re looking out from a high building. It’s the immediate spark of anger you feel when someone cuts you off, and makes you want to run your car into that moron. It’s the flash of fear in you when something surprises you at night, leaving you quivering with your body primed to fight or flee. Call it the hind brain, the subconscious, whatever: I’m not a shrink. But it’s there, and it’s real.

Mine wore a lot of black, even before Lasciel showed up.

Like I said. Chilling.

The fallen angel turned to depart on that note, probably because it would have made a nicely scary exit line.

I extended my hand, and with it my mind, and barred her departure with an effort of simple will Lasciel existed only in my thoughts, after all. “My head,” I told her. “My rules. We aren’t finished.”

She turned to face me, and her eyes suddenly glowed with orange and amber and scarlet flickers of Hellfire. It was the only non-black thing about her.

“See, here’s the thing,” I said. “My inner evil twin might have a lot of impulses I’d rather not indulge - but he isn’t a stranger. He’s me.”

“Yes. He is. Full of anger. Full of the need for power. Full of hate.” She smiled, and her teeth were white and quite pointy. “He just doesn’t lie to himself about it.”

“I don’t lie to myself,” I responded. “Anger is just anger. It isn’t good. It isn’t bad. It just is. What you do with it is what matters. It’s like anything else. You can use it to build or to destroy. You just have to make the choice.”

“Constructive anger,” the demon said, her voice dropping sarcasm.

“Also known as passion,” I said quietly. “Passion has overthrown tyrants and freed prisoners and slaves. Passion had brought justice where there was savagery. Passion has created freedom where there was nothing but fear. Passion has helped souls rise from the ashes of their horrible lives and build something better, stronger, more beautiful.”

Lasciel narrowed her eyes.

“In point of fact,” I said quietly, “that kind of thing really doesn’t get done without passion. Anger is one of the things that can help build it - if it’s controlled.”

“If you really believed that,” Lasciel said, “you’d not be having any anger-control issues.”

“Because I’m perfect?” I asked her, and snorted. “A lot of men go a lifetime without ever figuring out how to control anger. I’ve been doing it longer than some, and better than some, but I don’t kid myself that I’m a saint.” I shrugged. “A lot of things I see make me angry. It’s one of the reasons I decided to spend my life doing something about it.”

Harry Dresden and Lasciel, The Dresden Files 09: White Night by Jim Butcher.