ACT IV, SCENE 4, LINES 28-30
"This is th' impostume of much wealth and peace,
That inward breaks and shows no cause without
Why the man dies."

Hamlet is talking to Fortinbras' captain about the land, which has been symbolically given to Norway to prevent them from invading Denmark.  This statement is however, also descriptive of Hamlet's own condition.  The events that have caused his madness fester inside him like an abscess or tumor.  The cause is unseen by others though it is destroying him inside. 

Theme Analysis

The true nature of Hamlet's madness has been an issue of debate for scholars over the centuries.  One theory is that Hamlet's madness was for his own protection.  In the time period in which Hamlet would have lived, governments functioned through the usage of intricate spying networks.  In Hamlet's Denmark, no one is permitted to go unwatched.  Rosencrantz, Guildenstern, and Polonius are all sent to spy on Hamlet at various times. Polonius meets his death in the process.  When Hamlet discovers the atrocity committed by his uncle, he wishes for revenge.  In that time, it would have been quite natural to take matters into his own hands.  In order to keep his plans secret; he cannot let on that he knows of the crime.  Since he is constantly being spied upon and having his actions and words reported to Claudius, he must act enigmatically.

Shakespeare puts Hamlet into a situation in which he must deal with the betrayal and murder of his father by his own family members.  Communication of feeling is done solely in monologue or through the reports of a third party, or spy.  Hamlet must use the player's performance to observe the reaction of Claudius because the topic of the death of King Hamlet is not acceptable discussion material.  Therefore, Hamlet uses the performance to reveal the show that Claudius has been presenting to his subjects.  The problem is, the revelation is made only to Hamlet.  The people of Denmark know nothing of the ghost nor do they have any reason to suspect the reason for which the play is being presented.  Hamlet's mistake is that he has now alerted Claudius that he knows of the murder.  Claudius then can plot to rid himself of Hamlet, and therefore the danger of being found out. 

Following the presentation of the play, Hamlet loses his focus.  He is unable to exact revenge against Claudius when the opportunity presents itself.  Had he been able to kill his uncle while he was praying, the lives of Laertes, Gertrude, and himself might have been saved.  Instead, Hamlet becomes lost in his own psychological cloud, which highlights his inability to bring matters to a swift end.  Hamlet is a highly reactive character but does not ever seem to have a certain plan by which to accomplish his goal of revenge.  Ultimately, the characters of Shakespeare's Hamlet become victims of the unwholesome situation of their own creation.

Top Ten Quotes
1) Polonius to his son Laertes who is departing for France (1.3.84):
"This above all: to thine own self be true, And it must follow, as the night the day, Thou canst not then be false to any man."

2) Hamlet's description of the less-than-natural relationship between himself and Claudius (1.2.67):
"A little more than kin and less than kind."

3) Ophelia to her brother Laertes who is giving her advice on her relationship with Hamlet (1.3.51):
"Do not, as some ungracious pastors do, Show me the steep and thorny way to heaven, Whiles, like a puffed and reckless libertine, Himself the primrose path of dalliance treads And recks not his own rede."