Tragic means sad on a grand scale. Rain on your parade? Sad. Weeks of rain leading to the destruction of a small town and the lives of those in it? Tragic.
Though the word tragic has come to be used for common sorrows, it's best reserved for the kind of sad, unavoidable situations that Shakespeare would have written about. In a staged tragedy, the main character comes to a sad end due to his or her one tragic flaw –– this lead is called a tragic hero.