Read the excerpt from Utopia. The Utopians wonder how any man should be so much taken with the glaring doubtful lustre of a jewel or a stone, that can look up to a star or to the sun himself; or how any should value himself because his cloth is made of a finer thread; for, how fine soever that thread may be, it was once no better than the fleece of a sheep, and that sheep, was a sheep still, for all its wearing it. They wonder much to hear that gold, which in itself is so useless a thing, should be everywhere so much esteemed that even man, for whom it was made, and by whom it has its value, should yet be thought of less value than this metal . . . What is the central idea of this excerpt?