Hamlet's downfall is his tendency to procrastinate, and this weakness destroys his ability to act with decisiveness and impact. He is also generally indecisive and fickle in his emotions. Some interpretations of the play claim he also has an Oedipus complex, which causes his feelings about his mother and Claudius to become exaggerated and fill him with self-loathing and anger. These emotions build up and bring him to a state of anxiety wherein his words often contradict his earlier actions or speeches, making him inconsistent and unreliable.
He plays out his own guilt over his inappropriate affection for his mother by focusing on Claudius' guilt, confessed to him in a dream of a ghost, and this focusing on revenge further prevents him from achieving self-knowledge. He also struggles with thoughts of suicide when he becomes overwhelmed by his conflicting emotions, and wishes to hide from his problems.
His unstable emotional state causes him to speak without thinking often. But being very self-aware, Hamlet also tells people what they want to hear and this causes difficulties for him. This is most apparent in his dealings with his lover Ophelia; he is affectionate and loving with her, but then dismisses her with cruelty. In Act 3, Scene 1, immediately after his soliloquy wherein he considers killing himself as a possible solution to his problems, a worried Ophelia comes to him and is met with abuse and mockery. His treatment of the woman he loves is another example of his conflicted emotions and his inability to remain focused and consistent.