What quotes best highlight the key elements of tragedy in Shakespeare's Othello

A short but tragic quote spoken by Othello from act 2, scene 3 is the following, which underscores a key element of the play's tragedy:

Iago is most honest.

Much of the unfolding tragedy can be pinned to Iago's ability to deceive Othello about the kind of person he really is: maliciously bent on destroying Othello. One of Othello's flaws is how he is blinded and manipulated by this man. By the third act, we as the audience know how completely despicable Iago is—in part because he tells us so—and can only react in helpless horror as Othello is deceived.
Another key point of tragedy is that Othello's awareness of Iago's evil comes too late, after Desdemona is dead. Again, a simple line of anguish communicates Othello's deep distress at his own misinterpretation of events and misplaced trust. In act 5, scene 2, he says of himself:

Oh Fool! Fool! Fool!

Sadly, while we sympathize with Othello deeply, he is right that he was foolish.

At the end of play (also in act 5, scene 2), Othello advises Lodvico that he must tell the story of what happened. Othello says:

. . . must you speak
Of one that loved not wisely, but too well.Of one not easily jealous, but being wrought,Perplexed in the extreme. Of one whose hand,Like the base Indian, threw a pearl awayRicher than all his tribe . . .

Here, Othello reveals another central element of his tragedy: he loved Desdemona too much and, at the same time, wasn't secure enough about himself to believe she could love him back. He shows his awareness that he was manipulated and reveals the insecurity brought on by his blackness when he says that Desdemona was a "pearl" (which is white) richer than all his "tribe."