Revenge is sweet indeed
Act IV, Scene 4, Lines 31-65
Hamlet is confused and frustrated with himself. He does not understand why it has become so difficult to kill Claudius. The source of his anger is not explicitly directed at his uncle, but instead, is directed at his own lack of progress and the numerous times when he could not kill Claudius. Too many has he been blinded by his thoughts, schemes, and fickle decisions, that he realizes he should have been more focused on the problem at hand, the revenge. He displays contempt for his passiveness and subordination towards people around. This is caused by his insecurities that is depicted in his "To Be or Not to Be" Speech in Act III.
Hamlet in this speech brands himself a coward, a mere base beast. This speech displays Hamlet's true reasons for murder, Hamlet exacts revenge for his honor, not only for his father. Honor, as Hamlet puts it, is the only thing that stands between being a man and not. Since Hamlet's thirst has been yet vanquished, he continues to strive and live, assuring himself that he shall never again contemplate suicide. He becomes greatly disappointed in himself after this revelation, lecturing himself that God need not create lazy men, that there is no place or need for lazy people in this world. Comparing himself to Fortinbras's army, Hamlet decides that his only goal is to remain a man and claim back justice for his father. The honor that both these men want causes them to stop at nothing in order to get what they want, for Hamlet, it is revenge, and for Fortinbras, it is Denmark. Both men have their pride damaged, Fortinbras by his father and Hamlet by his uncle. This portrayal of humiliation is what fuels the ambition and motivation for these men to persist their goals: revenge.