Iago is able to mislead and misdirect his listeners because he understands what the people around him need to hear.  Iago is brilliant in understanding character motivation.  No other character in the play is so attune to context and individual motivation.  Iago is able to use circumstance and character to fully ensure that his listeners do what he wishes them to do without even knowing it.  It is through this insight into people that he is able to manipulate others into doing his bidding.  The manner in which Iago is constructed is done so without any long term goal or vision.  Rather, Iago is just a force of malevolence or one that is perpetually angry.  It is such a condition that allows him to perfectly design where individuals should be in order to be the most unhappy, matching his own personal state.  In this light, Iago is able to mislead others, pretending to provide truth, but enabling his own ends of transgression to be met.  We see throughout the play.   For example, Iago uses the vision Roderigo has of a union with Desdemona to manipulate Roderigo. Cassio is a man driven by the need to maintain outer appearances, and he easily accepts Iago's advice that he recover his rank by going through Desdemona. Iago also uses to his advantage the fact that Desdemona is of a kind and generous nature, one who will gladly accept the opportunity to persuade her husband to make amends with his lieutenant. And, finally, Iago uses Othello's jealous nature and his apparent insecurity to convince Othello of Desdemona's infidelity.