what line of reasoning is followed by the Prince of Aragon in making his choice of casket?

The Prince of Aragon rejects lead because of the ominous warning, and thinks that gold refers to the foolish populace. Instead he chooses silver which indicates he will receive what he deserves. The Prince takes the key and opens the casket to reveal a "blinking idiot" (2.9.53). The scroll indicates that those who are self-loving deserve to be called idiots, and would not make good husbands for Portia. The Prince is upset by his choice, but is forced to leave.