Several characters in Othello go to extremes to restore their honor and attain some sense of certainty about their lives and positions.
Iago is a prime example. He despises Othello because he feels that Othello has wounded his honor by passing him over for the role of lieutenant and giving the position to Michael Cassio instead. Iago is now determined to ruin both Cassio and Othello (not thinking that such action would actually put him out of a job altogether!). Iago concocts several schemes to serve his purpose, including discrediting Cassio by the fight with Roderigo and, even more seriously, making Othello believe that Cassio and Desdemona are having an affair. Iago is determined to promote himself over everyone else and make his enemies suffer. He wants to be certain about that.
Cassio ends up bewildered and completely uncertain about anything in his life. He is, of course, innocent of starting the fight with Roderigo (which is set up by Iago) and of any misconduct with Desdemona. Yet Othello fails to investigate fully, believes Iago's unfounded accusations, and strips Cassio of his position. Cassio, also misled by Iago, goes to Desdemona only to try to restore his honor and assure Othello of his loyalty, but that, of course, backfires.
Othello, for his part, seems to be uncertain about everything in his life, except perhaps Iago (a misdirected certainty indeed!). He does not trust Cassio, nor does he trust Desdemona even when she heartily pleads her innocence. He is, apparently, insecure in his relationships, and that could come from his shaky position in society as a Moor. This makes him all the more suspicious and uncertain of where he stands with anyone, but of course, he also has a major problem with pride, so much so that he ends up killing his own wife rather than listening to what she has to say and getting to the bottom of the situation. In so doing, he dishonors himself far more than anyone else ever could.