Tom makes an important discovery in Chapter 2, that if we want to make someone want something, we need to make that thing appear to be difficult to get.  At the end of the Chaper, the narrator tells us, "He had discovered a great law of human action,...that in order to make a man or boy covet a thing, it is only necessary to make the thing difficult to attain (Twain, 16). In other words, Tom discovered the law of supply and demand!

Tom makes this discovery by pretending that whitewashing a fence is such a desirable activity that people should want to compete to do it.  As a result of this manipulation, he collects a number of "treasures," and at the end of the chapter he see this as a "substantial change" in his "worldly circumstances." (Twain, 16.)