Stock Backstory for a character. Much like a Mysterious Past, except more tragic and troubled. Don't expect it to be revealed all at once, or sometimes at all. It usually gets revealed in small doses through a Troubled Backstory Flashback as the story progresses; possibly in a Flashback Nightmare where a happy memory transforms into a slaughter. Often used as a Freudian Excuse for an antisocial character's Jerkass tendencies or quiet stoicism. Still, it is understandable that the character wants to keep it secret because They're Called "Personal Issues" for a Reason, after all.