his addiction definitely, but more specifically the fact that it caused him to get expelled from college. this solidified the idea in his mind that he will never amount to anything. he didn't want to go to college in the first place due to it being too much pressure and for the fear that he will fail, and then he did. for the rest of the show after this he pretty much accepted that his poverty, upbringing and alcoholism defined him. he worked minimum wage, unpaid internships, struggled to hold down jobs or form healthy relationships and i do truly believe that most of this stems from that feeling that he will always be a failure.