According to the Aristotelian view of tragedy, a tragic hero must fall through his or her own error. This is typically called the "tragic flaw", and can be applied to any characteristic that causes the downfall the hero. Shakespeare's Hamlet, Prince of Denmark can be seen as an Aristotelian tragedy and Hamlet as it's tragic hero. Hamlet's flaw, which in accordance with Aristotle's principles of tragedy causes his demise, is his inability to act. This defect of Hamlet's character is displayed throughout the play.
In the opening scenes of the play, the Ghost of old Hamlet reveals the truth about his death to his son, and tells Hamlet to avenge the murder. Hamlet's first response is one that sounds of speedy action, saying "Haste me to know't that I with winds as swift" May sweep to my revenge." (p. 34 lines 29-31) Unfortunately, Hamlet's inability to act on his father's extortion has him reluctant to kill King Claudius by the end of that very scene, when he says, "This time is out of joint, O cursed spite, that I was ever born to set it right." (p. 41 lines 190-191).
As the play goes on, Hamlet still has yet to act on his murderous task. In act II, scene 2, Hamlet decides that, before he can avenge his father's death, he must make sure that the Ghost was telling the truth. This simply gives Hamlet more excuse to procrastinate-he gets to put off killing Claudius until after the "play within a play", Mousetrap, is preformed. Not surprisingly, Hamlets inability to act gets the best of him even after he has obtained his proof that Claudius is guilty, and he can only contemplate the act.
Further evidence of Hamlet's tragic flaw can be found in act III, scene 3. At this point, Hamlet is sure of Claudius' guilt, and has even declared that "Now could I drink hot blood and do such bitter business as the day Would quake to look on." (p. 99 lines 406-408) He comes to find King Claudius alone, and recognizes it as an opportunity to act, but almost immediately talks himself out of action on the bases that the King is praying, and will therefore go to heaven.