Maintaining one's reputation was a powerful motivator in Shakespeare's day and men would kill in the name of 'honor.' Iago indicates to Othello that
reputation ... is more important than money. Riches can be taken away easily, yet their loss is recoverable. But if one’s reputation is taken away...
We see Iago and his obsession with reputation and also his cunning - he knows that reputation is precious so he can tarnish Cassio's good name and get what he wants at the same time. He is a master manipulator. Reverse psychology is a favorite method of his, making - mostly - Othello reach his own conclusions.
Who steals my purse steals trash (III.iii.157)
Obviously questioning someone’s good name would require more than just petty jealousy - a flaw Iago readily admits to. He warns Othello to rather trust his own observations.
Even at the end of Othello, Othello himself is obsessed with maintaining his reputation as a military man who has served his adopted homeland well, despite what other despicable things he has done:
I have done the state some service, and they know't—
Othello even suggests that he is somehow 'saving' Desdemona's reputation - as she apparently shames herself- by killing her:
I can again thy former light restore
Jealousy (and therefore the loss of trust)is another strong theme running through Othello. It drives the characters to do unspeakable things. Again, it is Iago who uses the weaknesses of others to his best advantage, stirring the jealousy within. He
is able to twist the distinction between what something is and what it appears to be, and it is this deception...
that leads to a complete loss of trust even when there is no grounds for it. Even though Othello does not believe it
Give me ocular proof (III.iii.360)
it will not take much for him to doubt the most virtuous person especially as the seeds have already been sown by Desdemona's own father when he describes her apparent 'betrayal:'
Look to her, Moor, if thou hast eyes to see;
She has deceiv'd her father, and may thee (I.iii.292-293).
The loss of trust is made even more poignant by Othello's misplaced trust in Iago. Othello is so deceived by Iago that, not only does he leave his wife in Iago's 'charge' but he does not even believe Emilia when she tries to warn Othello.
My friend, thy husband, honest, honest Iago (V.ii.155).
Refer to the eNotes guides where there are many examples to confirm and support these issues.
Othello is also about a loss of self and a loss of self-worth. We know how important military success was to Othello and is he very proud of his conquests and his own worth. However, he
wrestles with himself while on the verge of smothering Desdemona in the final scene of the play:
It is the cause, it is the cause, my soul,
Let me not name it to you, you chaste stars!
It is the cause. (V.ii.1)
Othello's confusion cannot be fathomed. He tries to justify the killing of Desdemona to save her good name and kills himself when he realises what he has done. He no longer knows who he is. Nothing will change the fact that Othello is an 'outsider' and his obsession with needing to constantly prove himself has led to this irrational event thus culminating in the loss of pride in himself and the loss of his 'hero' status.
..a malignant and turban'd Turk
Beat a Venetian and traduc'd the state,
I took by the throat the circumcised dog
And smote him—thus.
Even to the end, he needs to remind others of his worth.