For both Iago and Hamlet, the initial emotion is resentment.
However, there is a big difference between them. Othello denied Iago the rank of lieutenant – this rejection superimposed itself onto Iago’s envy of the aristocrats in general, i.e., his desire to become one of them. This envy is in fact the driving force; the rejection is rather used as a pretext. Iago is certain inside himself that he deserves a better position. He is confident in himself and his ability to take revenge. Iago is a self-made man. He knows how to set a goal and how to achieve it.
For Hamlet, the death of his father knocked the ground from under his feet. He was not accustomed to pursue his own in life, and “the feeling of nothingness” (quote by Goethe) is what leads him to resentment. Ultimately, Hamlet gets stuck in his resentment, while Iago quickly transforms it into anger and hatred.
Hamlet is indecisive. We see that once he has already collected all of the proof of the king’s guilt that he required, he stalls… so what is he waiting for? Why does he agree to a fencing contest with Laertes? Only in the face of death, when he realizes that he has just moments left to live, does Hamlet become decisive.
Iago does not hesitate. He hatches a plan for exacting his revenge and he implements this plan with calculation and precision. His hatred transforms into action. His emotion is not suppressed, it is expressed. As a result, unlike Hamlet, Iago does not have emotional outbursts (an example of Hamlet’s would be when he killed Polonius); Iago acts methodically and in cold blood.
Iago stands much higher than Hamlet on the emotional energy scale. Hamlet is hampered by his emotions, which do not end at resentment (suppressed anger). An awareness of his own indecisiveness, and, as a result, anger towards himself (the feeling of guilt) is also present in him. Hamlet’s emotions prevent him from acting, and when he does, his actions turn out to be the actions of a weak and indecisive person.
Iago’s emotions, on the contrary, push him to action. His hatred (and envy) is an unyielding force that does not let him deviate from his path even for a minute.
It may seem strange that I put Iago’s hatred above Hamlet’s indecisiveness. But energy has nothing to do with morality. Emotions are a force; their purpose is to push us into action. Iago’s emotions fulfill their purpose, Hamlet’s emotions do not.
Of course, hate is not the best of emotions. Iago also had the opportunity to choose another emotion. But the emotion that is realized is always stronger than the emotion that is suppressed.
Iago chose the emotion of hate as his guide. Hamlet, most likely, would not have done so in his place. Hamlet as an individual stands much higher than Iago, for his beliefs (of which we know from Hamlet’s monologues) are much higher than Iago’s beliefs. But Hamlet’s lack of confidence in himself, his sense of worthlessness, ruins everything. In fact, Hamlet is torn between different beliefs. The feeling of worthlessness is energetically below hate. And again, this is not a question of morality, it is a question of energy. Iago was able to achieve integrity and a resonance between beliefs and emotions. His beliefs and emotions match. This gives Iago strength – the strength of action.
Meanwhile Hamlet reveals a tragic discrepancy between different beliefs, as well as between beliefs and emotions. Different beliefs cause different emotions, and he does not know which of them to follow, as they pull him in different directions. The root cause lies precisely in the contradictions between the various beliefs within Hamlet, and not at all in the indecisiveness of his character, as several generations of critics would have it. On the contrary, the indecisiveness of character is a consequence of the rift between different beliefs within Hamlet. What does he want? Does he want to kill Claudius out of a sense of duty, or to be a prince and heir to the throne, or to flee from Denmark (a prison, according to his words), or just to bury his head in the sand and do nothing? Does he want to be a private citizen (he extols Horatio’s independence from the court), or the prince and king (in the scene in Ophelia’s grave, he calls himself ‘Hamlet the Dane’ (with a capital D – it was custom to denote people of royal blood in this way))? Incidentally, a minute before this he talks about the futility of fame and power, explaining that ‘the noble dust of Alexander (the Great)’ may be found ‘stopping a bung-hole’ (in a beer-barrel).
Iago most likely also had different beliefs: we always have a choice. Iago’s choice – hate and revenge – is the low choice on the energy scale of beliefs. But having made this choice, he does not hesitate; therefore his emotions are strong and uninhibited.
Frank Underwood, the hero of the “House of Cards” series, is a modern Iago. The president offended him by not giving him the promised post of Secretary of State, and Frank chooses the path of revenge. His beliefs and emotions work in resonance, so his actions are extremely effective.