"I'm glad you figured it out [blank] because until you did killing wouldn't be half as much fun!"
This possibly misremembered quote is all I have to go on, but now I have remembered it's bothering me I can't figure out what it's from.
It's a confrontation between the hero and the villain, with the villain having had a part in the protagonist's tragic backstory (probably killed parents) that the hero either forgot or had to learn. I feel like it was from an animated project, though I couldn't say if it was a movie or show.