As a result of his feelings for Desdemona, Roderigo is very jealous of Othello. Roderigo's jealousy clouds his judgement, and causes him to make very bad decisions. An example of an irrational decision from Roderigo is when he listens to Iago, and sells all his assets, "put[ing] money in [his] purse" (I.iii.338) in an attempt to follow Desdemona to Cyprus. Iago knowing full well of Roderigo's love for Desdemona offers to help him win her over, secretly taking advantage of him for his money as well as getting Roderigo to do his dirty work. Roderigo only realizes this when it is too late, not only has he lost everything but nor does he win Desdemona's heart. Showing yet again the destructive influence jealousy has on the human mind. .
Jealousy and its destructive influence in making irrational decisions is also shown by Othello. Iago tells Othello that he suspects Desdemona of infidelity, pointing out that Desdemona and Cassio are too close with one another and that it is very likely they are sleeping together. Othello at first takes the news lightly, however it is quite clear that the idea of an affair is bothering him a lot. This is especially apparent when Othello returns, this time completely consumed with jealousy. The idea of an affair has eaten away at his soul so much that he willing to kill Iago, should he fail to "prove [Desdemona] a whore" (III.iii.359). Announcing the murder of another person based solely on gossip is absurd, and shows the depths of destruction jealousy has caused. Othello has already proven that he is willing to kill Iago, and has now become an unstable person. Othello's mental instability has gotten greater as the play goes forward, however the biggest irrational decision made, fueled by jealousy is when he plans and carries out Desdemona's murder. Iago is able to convince Othello of the false affair, by showing him his handkerchief in Cassio's possession.
