"Knavery's plain face is never seen till used."

       Iago states that he is not what he appears to be, and only does things for his personnel gain a multitude of time towards Roderigo. Yet as sly as he is, he manipulates him to do things for his personnel gain and goals while keeping Roderigo blinded by his lust for Desdemona. In doing so, Iago also goes around and becomes close friends with Othello and Cassio while doing the same things to them, but for alternative reasons.
        For example, Iago hates Cassio for taking what he felt was rightfully his, the lieutenant rank given to him. With that rank given to Cassio, it makes Iago furious and then ultimately has him plan to get rid of Cassio. Yet on the other hand is Othello, who Iago also envy's and hold responsible for taking his wife from him. So the whole time within the book, Iago becomes close and appears very honest to Othello in which he abuses that relationship with him and 'twixts' his mind. Iago tells Othello that Desdemona is cheating on him with Cassio only to enrage him to do something irrational, such as plan to kill her and Cassio. When that is established, Iago states that he will take care of Cassio in which he again uses Roderigo to answer him. Therefore, Iago's plan was,"look out for number one" meaning he is only after whats important to him and he doesn't care who he has to lie to do it.