This is Teresa's "curse" that Nostromo later takes to heart, and to avoid which he steals the cargo of silver. But if character is the true treasure, then Teresa's curse comes true, for by stealing the silver Nostromo is bereft of the purity of character he possessed before. Note that, the voice of class-conscious material welfare having spoken, whatever choice Nostromo makes about the lost silver is a "folly," and will betray him into poverty of one sort or the other.