In establishing what Portia calls (Act II, Scene 1) “the lottery of my destiny,” her father removed much of her fate from her own decision. Because he was a good man as well as a wealthy man, he wanted to ensure that his daughter would remain well-off after he passed away. He also adhered to the predominant idea of the day (and one of the play’s themes), that love makes lovers do foolish things. Because Portia’s husband would have access to her fortune, he created the three caskets with very different exteriors. He apparently reasoned that their relative appeal to the suitors was likely to attract the right kind of man. It also seems, throughout the play, that everyone believes in fate so that the outcome may be considered predetermined.
Portia is a smart, sensible young woman. As she is proper and not rebellious, she is not necessarily happy about her father’s decision, but she is committed to abide by it.
In act I, scene 2, in her first conversation with her maid Nerissa, the two women discuss the topic extensively. Portia laments that she can neither choose nor refuse, "so is the will of a living daughter curbed/ by the will of a dead father.” Yet she does commit to abiding by his wishes:
“If I live to be as old as Sibylla, I will die as
chaste as Diana, unless I be obtained by the manner
of my father's will.”
Portia’s father, Nerissa notes, was “ever virtuous,” and as a holy man, he had a good inspiration; she has confidence in the idea that the correct chooser will be the one who truly loves Portia.
that he hath devised in these three chests of gold,
silver and lead, whereof who chooses his meaning
chooses you, will, no doubt, never be chosen by any
rightly but one who shall rightly love.
Portia also subscribes to the dominant idea that love clouds the judgment. At the point when the man she loves is about to make his choice, she comments: “O love,/ Be moderate; allay thy ecstasy,/ In measure rein thy joy….”
Although his method is unusual, it turns out that her father had the right instincts, as revealed by the messages inside the caskets when opened. The gold message speaks about falsity and greed, and the silver one criticizes vanity.
Bassanio, who correctly chooses the lead casket, is the one who had figured out the clue that appearances are deceiving: “So may the outward shows be least themselves:/ The world is still deceived with ornament.” When he opens the lead casket, that is precisely the message. “You that choose not by the view,/ Chance as fair and choose as true!”