Othello suspects Desdemona of infidelity about four hours after she meets Cassius. I no gets it.
Odd, right? But arguably, this says TONS about Othello's insecurities. He's an alien mercenary, the Venetian flavor of the month: he's an outsider with no secure, innate place in Venetian (or European!) society, and his marriage to Desdemona only intensifies his outsiderness by contrast. He seems to see himself in an permanently fragile position ... as a man, as a soldier, and as a husband. He's always LOOKING for cracks under his feet in all these arenas, and always will. His near-instant suspicions of cuckoldry are right in character. Iago's genius was to spot this quality in Othello, and exploit it like a skilled demolitionist.
Build up of his concerns over their marriage. In the first scene we see that age and race are something that makes their relationship difficult, and Othello obviously feels insecure because of this. Compare Othello to the typically Venetian (well, Florentine...but close enough) Cassio who, in the context of the play and the context of the time, would make a better husband for Desdemona. By the time they're in Cyprus, the Turks have been defeated leaving Othello with no way to prove himself since there's no outright military threat. This is a threat to his manhood as he has reached his high status through the military but that has now been taken away from him, and the only remaining way for him to prove himself is through his romance with Desdemona. Unfortunately, he is already threatened by Cassio's presence and he is constantly interrupted whenever he and Desdemona have the chance to be intimate. These things may also cause him to doubt his ability as a lover. At this point his two identities in the play (lover and soldier) have been challenged, leaving him as an exposed and vulnerable person. Iago capitalises on this, and we see Othello jumping to rash conclusions with little to prove them.
She had met Cassio before, though. Othello himself said that Cassio would take messages between he and Desdemona before they were married. He had been around both of them during much of Othello's courting of her. (Act 3, Scene 3, lines 94-100)
Brabantio's words to Othello (which can be see on the main page) were probably also playing on his mind.
To the original poster: Shakespeare sometimes plays havoc with timelines. For example, Romeo and Juliet takes place over the course of three days, when the story it was based off of was stretched out over more like three months. There's conflicting evidence as to how much time passes between Othello and Desdemona's wedding, their move to Cyprus, and when Iago starts to put his plot in gear. But most scholars agree that there's meant to be a timeskip of at least a month between one act or another. That or the entire play took place over the course of a weekend.
Pretty much the entirety of Othello bugs the crap out of me, for the following reasons:
Iago's cunning and savvy would, if channeled productively, make him a far superior General to Othello, never mind a better Lieutenant than Cassio.
Harold Bloom described Iago as a kind of "moral pyromaniac": even before being passed over, he was the sort of fellow who couldn't stop waging war, who'd rather burn the world down than give an inch. This made him the perfect "ancient," or ensign (you're supposed to die rather than let the general's banner be taken). However, a general and field officer have to know the limits of war, including when/how to look for and negotiate a peace.
Cassio is a drunk with no field experience who is given the job by Othello for quite arguably nepotistic reasons (Cassio acted as the go-between in Othello's wooing of Desdemona).
Disagree with 'drunk". Cassio is very reluctant to drink - sure, Iago persuades him, but Iago is pretty much a force of nature.
Cassio has no field experience but he is a great theorist, which would be useful in the lead-up to battle.
Othello is a stone idiot. I wouldn't have him in charge of an ice-cream stand, never mind an army.
Generally, these points were quite common in the period. Nepotism was used frequently throughout any Army in the period and Othello's choice was his own. Iago was born of a common stock and so would have been unable to advance much further than he already had. Othello did have an advantage in this regard by being of Royal blood, someone who had later become a mercenary before earning his trusted position in the council's eyes. Although we don't get to see Othello commanding an Army, we do see him going about his regular duties and is spoken of highly throughout. Just because he loved too well outside of battle, doesn't mean he's incompetent in it.
Why on earth does Desdemona die? She's kind of half-dead, then comes back to life to make her final comments, then dies again. The major problem? She was killed by being smothered! If she didn't die when she was being smothered, it makes absolutely no sense that she should die again after the murder weapon was removed!
Rule of Drama. It's a play, main characters who die get final speeches even if it makes no sense.
Why didn't Othello just... ask Desdemona about the whole thing?
Why? She'd just 'lie' about it anyway. ("She has decieved her father, and may thee.") Also worth noting that he does ask about the handkerchief when Desdemona is trying to get him to reinstate Cassio. So yeah.
And she's doing this after he just found the hankie in Cassio's room. Face it, poor girl was screwed in every sense of the world.
When Iago enters and is asked by Emilia if he told Othello his wife was false, why does he back up Othello's story, thus basically exposing himself as the real villain? He could have feigned innocence and denied having said anything to Othello. (Sure, he would still have been exposed anyway later on by Rodrigo's letter, but he couldn't have known that.)
Iago doesn't admit guilt at first. What he tells Emilia is that he told Othello "only what he thought was happening". In this way, he could claim he was innocent of the plots by insinuating that he never actually told Othello that Desdemona cheated with Cassio but only that he thought Desdemona had cheated.