These are wise words from Cecily Herondale from Clockwork Princess or well technically Cassandra Clare since she did create the character.
"I think," she said, choosing her words with care, "that any good impulse can be twisted into something evil. Look at the Magister. He does what he does because he hates the Shadowhunters, out of loyalty to his parents, who cared for him, and who was killed. It is not beyond the realm of understanding. And yet nothing excuses the result. I think when we make choices--for each choice is individual of the choices we have made before--we must examine not only our reasons for making them, but what result they will have, and whether good people will be hurt by our decisions."
She then goes on to say, "Do not regret too much choices you have made in the past, Gabriel," she said, aware that she was using his Christian name, but not able to help it. "Only make the right ones in the future. We are ever capable of change and ever capable of being our better selves."
FYI the girl in the photo is Alexandra Daddario, Matthew Daddario's sister who plays Alec Lightwood. Weird how I think she would be perfect for Cecily Herondale.