In The Merchant of Venice, how does Portia encourage the prince of Morocco when he displays his vanity?

The verbal exchange between the prince of Morocco and Portia occurs at the beginning of Act ll, Scene 1. The prince has obviously arrived to chance his luck to win Portia's hand by participating in the lottery her deceased father concocted. The prince blathers on about his greatness and asks Portia not to discriminate against him because of his darker complexion. He comes across as quite boastful and conceited.
Portia's retort encourages him. She informs the prince that her choice for a husband is not limited only to what she might see as attractive but that the lottery bars her from making any choice whatsoever. In this sense, then, the prince has as much a chance as any of her suitors.
In response, the prince thanks Portia for her kind remark and begins bragging again about his prowess as a soldier and the quality of his courage—all skills he would use to win Portia's heart. He alludes to characters in Greek mythology when making the point that just as Hercules might lose a sought-after prize to a weaker man in a lottery because of destiny, he too could lose out on winning Portia's hand. The prince evidently deems himself the equal of Hercules and Alcides, both heroic characters in Greek literature. He states that he would die of grief if he should, similarly, lose Portia to a lesser man.
Portia informs him that he should take his chance or decide not to choose. If he does choose and loses, he is forbidden from ever approaching another woman in way of marriage, since this is one of the requirements of the lottery. The prince accepts and is eager to try his luck. Portia stays him and advises that they must first proceed to the temple where he would have to make a solemn oath to abide to the conditions of the lottery. He can then try his luck after they have had dinner.