This line reveals that he is set on getting revenge for being betrayed and thus, has become a goal. It is his goal to get revenge so even when Desdemona after insists that she has done nothing wrong, Othello tells her to confess thee freely of thy sin (5.2.61) and that even if she denies it all, it will not change his mind, as he makes clear by telling her Thou art to die (5.2.65). Othellos refusal to listen to Desdemona is what leads to his failure, for it was his goal to kill her no matter what she said and only after she is dead does he learn that she was actually innocent. Ironically, it is primarily how Desdemona behave towards Othello that makes him doubt her. After Cassio lost his position as lieutenant, Desdemona accepted the task of trying to convince Othello to forgive Cassio. The start of her obsession of getting Cassios job back is when Desdemona says herself that My lord shall never rest,/Ill watch him tame and talk him out of patience (3.3.23-24).
As a result, she would bring up Cassio quite often and became obsessed with getting his job back. Her obsession and insistence of helping Cassio is presented well when she asks Othello if he can talk to Cassio tomorrow night, or Tuesday morn. /On Tuesday noon, or night¦but let it not/Exceed three days (3.3.60-64). Her insistence is only elevated when she continues to talk about how good a person Cassio and how Othello should let Cassio be received again (3.4.91), even though Othello was demanding to see her handkerchief and was noticeably getting angry. As Desdemona said earlier on in the play, [she] shall rather die/Than give thy cause away, (3.3.27-28), which presents this obsession as goal that she wants to achieve no matter what, even if it means ignoring Othellos demands for a moment. She insisting too much on reaching her goal and as a result, ended up dying because of it. Iagos obsession is similar to Othellos in the sense that they both sought out revenge and similar to Desdemonas in the sense that they both take it too far, but Iago sought revenge on nearly everybody he came into contact with.
His want to make Cassio fall is apparent in the first scene of the play, when he says Mere prattle without practice/Is all his soldiership (1.1.12) in regards to Cassio being made lieutenant. It is evident that Iago is not satisfied with this outcome and plots to do something about it, as shown when he says I follow [Othello] to serve my turn upon him (1.1.44). It is established that Iago wishes to hurt Othello and Cassio in some way, which is only the beginning of his obsession of wronging others who he believes have wronged him. As the play progresses, we see that Iago has successfully gotten Cassio to lose his job and have Othello want to kill Desdemona. Othello even gives Iago the position of lieutenant, but Iago continues to use those around him as pawns. After being told by Othello that he must go kill Cassio, Iago talks Roderigo into killing Cassio instead, tell him I will show you such a necessity in his death that you shall think yourself bound to put it on him (4.2.247-49).
Later on, Iago says that whether [Roderigo] kill Cassio/Or Cassio kill him, or each do kill each other,/Every way makes my gain (5.1.12-14), which reveals that he only wishes to see his victims fall. This is finalized several lines afterwards with Iago says No, [Cassio] must die (5.1.24). He could have stopped after becoming lieutenant, but he decided instead to use Roderigo as a pawn once more and continued with his schemes. He tried to use anybody he could as pawn in his schemes, and this included Emilia as well. However, he did not account for Emilia to go against him in the end by admitting that [Iago] begged of me to steal [the handkerchief] (5.2.243).
This goal to continue wronging others until the end eventually brings Iago to his failure, as he bit off more than he could chew. As presented in Othello, there were many cases in which ones obsession led to their failure. Othello was set on killing Desdemona no matter what, Desdemona was set on getting Cassios job back no matter what, and Iago was set on exacting revenge on those he feels have wronged him no matter what, but the result was that things did not turn for the better. The idea that a character failure is brought upon them when their obsession becomes a goal is evident in the three cases that were presented.