How does the Duke advise Brabantio in Othello?
Observing Brabantio's distress over what he regards as the loss of his daughter in marriage to Othello, as well as the strength and genuineness of Othello and Desdemona's affections for one another, the Duke counsels Brabantio to accept the situation and to make the best of it. The Duke appears to share Brabantio's general opinion that the relationship is an unfortunate development; he describes it as a "mangled matter," and echoes commonplace racist assumptions of the inferiority of dark-skinned people when he says "If virtue no delighted beauty lack, / Your son-in-law is far more fair than black." But he nevertheless urges the old man not to make his loss greater by disowning Desdemona. "Men do their broken weapons rather use / Than their bare hands," he says, an analogy between warfare and domestic relations which eerily foreshadows the play's larger conflict, a career soldier's failed adjustment to married life.
He continues, "When remedies are past, the griefs are ended / By seeing the worst, which late on hopes depended." In essence, he advises Brabantio that there is no use in continuing to regret and suffer over what has already occurred; Brabantio should take comfort in the fact that "the worst" is behind him. But as Edgar tells us in King Lear ("The worst is not / So long as we can say 'This is the worst.'"), this is a fallacious line of thinking. Things can and will become far worse for Desdemona, and Brabantio is right to fear, though he fears for the wrong reasons. Neither he nor the Duke can possibly anticipate the malicious intent of Iago; Brabantio's empty fears that Desdemona has been deceived, spellbound, or corrupted by Othello will be reflected in an unexpected way as Othello is deceived, spellbound, and corrupted by Iago.
The Duke's final bit of advice urges Brabantio to regain what dignity and agency he can by "smiling" in spite of what has happened: "The robb'd that smiles steals something from the thief; He robs himself that spends a bootless grief." Once again, these words are unintentionally relevant to the larger Othello/Iago drama which occupies the remainder of the play. Iago, deprived of his expected military promotion, is the "robb'd" who, with perpetually growing self-satisfaction, steals from Othello everything that he has. Othello, on the other hand, is partly responsible for his own undoing, and "robs himself" in his "bootless" (useless) agony over Desdemona's suspected infidelity.