Demons feed on death and pain ...

Demons feed on death and pain madness,\
Demons feed on death and pain madness," Valentine said. "When I kill, it is because I must. You grew up in a falsely beautiful paradise surrounded by fragile glass walls, my daughter. Your mother created the world she wanted to live in and she brought you up in it, but she never told you it was an illusion. And all the time the demons waited with their weapons of blood and terror to smash the glass and pull you free of the lie.
 Cassandra Clare

Quotes from the same author

Simon looked from one of them to the other, and shook his head. When did you two get so buddy-buddy? Last night it was all, ‘I’m the most elite warrior!’ ‘ No, I’m the most elite warrior!’ And today you’re playing Halo and giving each other props for good ideas.
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 Cassandra Clare
I am one of the Clave. It's in my blood and bones. So tell me, if you're so sure this wasn't my fault, why is it that the first thought in my mind when I saw Abbadon wasn't for my fellow warriors but for you?" His other hand came up; he was holding her face, prisoned between his palms. "I know-I knew-Alec wasn't acting like himself. I knew something was wrong. But all I could think about was you.
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 Cassandra Clare
Jem seemed to look through her then, as if he were seeing something beyond her, beyond the corridor, beyond the Institute itself. "Whatever you are physically," he said, "male or female, strong or weak, ill or healthy--all those things matter less than what your heart contains. If you have the soul of a warrior, you are a warrior. All those other things, they are the glass that contains the lamp, but you are the light inside." He smiled them, seeming to have come back to himself, slightly embarrassed. "That's what I believe.
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 Cassandra Clare
Whatever you are physically,' he said, 'Male or female, strong or weak, ill or healthy -- all those things matter less than what your heart contains. If you have the soul of a warrior, you are a warrior. Whatever the color, the shape, the design of the shade that conceals it, the flame inside the lamp remains the same. You are the flame.
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 Cassandra Clare
This was Jace being brave. Simon thought, brave and snarky because he thought Lilith was going to kill him, and that was the way he wanted to go, unafraid and on his feet. Like a warrior. The way Shadowhunters did. His death song would always be this-jokes and snideness and pretend arrogance, and that look in his eyes that said 'I'm better than you'. Simon just hadn't realized it before.
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 Cassandra Clare