Poor Joey. No, wait, that's not right. Not poor Joey at all.
Even before his literal riches (his hundreds of thousands of dollars that he makes supplying rusty truck parts to the US military, and then the untold millions with his shade-grown coffee business), there's really not much for which we can pity Joey Berglund. This is a guy for whom everything has always gone exactly as he wanted it to. This is a guy who sees the terrorist attacks of 9/11 as a personal affront to his life, with no thought of how anyone else might have been impacted by the tragedy. We're not kidding – this is the guy who still makes his way to class the afternoon of the attacks: "Not until he reached the big auditorium and found it all but empty did he understand that a really serious glitch had occurred" (3.2.1).
As a guy for whom everything has always gone as planned, Joey pretty much does what he wants. That is, he takes for granted his entitlement to perfect freedom, with no thought for how that might affect anyone around him. There is a passage (about his infatuation with Jenna) that suggests Franzen intends for Joey to represent the worst instincts of the American people, the extreme logical conclusion of America's deification of "freedom":
Jenna excited him the way large sums of money did, the way the delicious abdication of social responsibility did, the way the embrace of excessive resource consumption did. (2.4.54)
Freedom from morality, freedom from empathy, freedom from responsibility.
So what happens when Joey embraces his most selfish instincts and follows this path? Well, to be honest, he ends up causing the people around him a whole lot of suffering. (Franzen may want us to draw connections here between Joey and Franzen's view of American foreign policy.) He strings Connie along while chasing other girls, taking for granted that Connie will just wait for him and make no demands on his commitment to her. He exploits his mother's devotion to him too, taking her money even while barely consenting to speak to her on the phone.
Even when he was a child, he refused all discipline and guidance from his parents (his father in particular), and loathed mowing lawns and shoveling snow, because it made him feel subordinate to the adults he was serving. So as a high schooler, he quickly became an entrepreneur, to remove his reliance on asking for money from his parents.
Joey's epiphany comes when he finally takes this sense of entitlement and privilege too far. Where does he find himself? In a hotel room in Argentina with the girl of his dreams…unable to get an erection and, ultimately, kneeling by the toilet bowl, looking for his wedding ring in a pile of his own poop. Plus he's lost his only friend, and pretty much every relationship he cares about, in chasing this girl who's awful to him and a job he knows is morally wrong.
Finally, Joey does the one thing he swore he'd never do: he gives up his perfect freedom and reaches out for his father's help. And becomes a much better man for it.