Answer:
When the story starts asking you to forgive or forget terrible things that the hero feels no remorse for.
Step-by-step explanation:
When a villain knows that he or she is doing a wrong thing, feels regret, and then does it anyway. When because of doing that, the villain loses something/someone precious. When in the end, he or she realizes the wrong choices when it is too late to attempt to make things right—but still tries to make them right anyway as best he or she can.And then dies in the end, aware of a wasted life, and full of regret.
OR
Well it really doesn't unless your definition of tragic hero differs from the literary definition. A tragic hero is a character that makes an error in judgement that leads to his undoing. This means that he may not be a hero in a traditional sense so the usual hero/villain dichotomy need not apply.