In chapter 6 of The Great Gatsby, what is ironic about Dan Cody?

The irony is that the lessons Jay Gatz learns from Dan Cody, far from helping him attain his goals, actually serve to seal his fate.

Gatz had already thought up the Gatsby persona before Cody appeared in his yacht, but, in meeting Cody, Gatz felt as if he had finally arrived in the sphere to which he belonged. For Gatz, “resting on his oars and looking up at the railed deck, the yacht represented all the beauty and glamour in the world.” Cody had earned his millions in mining; despite his gift for making the astute business deal, he was nevertheless "on the verge of soft-mindedness," an easy target for fortune-hunting women. Despite his money, Cody never acquired the polish of the truly upper class. He was "the pioneer debauchee, who during one phase of American life brought back to the Eastern seaboard the savage violence of the frontier brothel and saloon." Cody lacked the snobbishness of someone like Tom, which perhaps explains his willingness to take Gatsby aboard his yacht and, eventually, to trust him implicitly.

Gatsby is never able to make his outside appearance match his inner desires. Perhaps his problems—the lesson that Cody was unable to give him—are the "inner desires" themselves. In the end, the difference between Gatsby and Tom, perhaps, is the difference between wanting and having.