In this excerpt from his speech from Act 3, Scene 2 of Shakespeare's The Merchant of Venice, Bassanio considers the difficulties of opening the wrong casket and thereby lose his chance to satisfy Shylock's rules of the game to win Portia, with whom he has already fallen in love. The theme of choice and misdirection has become concrete in the form of the caskets in front of him. As he determines, as logically as possible, his choice he argues in these lines that in every aspect of human life, absolute value can be misleading:
There is no vice so simple but assumes/ Some mark of virtue on his outward parts: (3:2: ll. 81-82)
Bassanio, aware that the choice of caskets holds his and Portia's fate as true lovers, must choose between ornate and commonplace (leaden) caskets, and he begins logically to second guess the nature of the caskets, comparing them to human beings who are fully of vices but are able to disguise those vices so that they appear to be virtues--just as the beautiful casket may contain nothing of value, and the leaden one may contain Portia.
His analysis is both thorough and logical as he continues to examine the parallels between humans and the caskets, which are, in a sense, substitutes for humans: if he chooses correctly, he gets Portia; if not, nothing:
How many cowards, whose hearts are all as false
As stairs of sand, wear yet upon their chins/ The beards of Hercules and frowning Mars;/ Who, inward search'd, have livers white as milk;/ And these assume but valour's excrement / To render them redoubted! (3:2:83-88)
Here, he is comparing the ornate caskets to cowards who grow beards in order to look like what they are manifestly not--Hercules, a demi-god and the strongest man of Greek mythology and Mars, the Roman god of war. Bassanio goes on to note that if one looks into these men who masquerade as heroes and gods one finds "livers white as milk," sure sign of a cowardly nature, but outwardly they look brave and strong--just as ornate caskets look like they contain something of value.
In sum, this section of 3:2 is Bassanio's way of analyzing the relative value of the caskets and using his understanding of human nature allows him to conclude that things of value can appear to be worthless and, conversely, valuable-looking caskets, just like valuable-seeming human beings, can be worthless. One can argue that Bassanio threads the maze of choice and value in this passage.