Nick's Cardinal Virture

At the end of chapter 3 Nick tells us our cardinal future by saying "I am one of the few honest people that I have ever known". Now to start a cardinal virtue is natural moral of typically prudence (cautiousness), justice (fair/reasonable), temperance (voluntary self-restraint), and fortitude (courage from pain/perseverance). So Nick's cardinal virtue is kind of a mixture of prudence and justice I think because like how the book mentioned at the start, people confide their secrets with Nick but they are not always the truth so he has to constantly stay cautious of his perspectives on people from different rumors since he all the secrets he has been told can be a mixture of truths and false. Now to the reader Nick seems like the only person we can truly understand from this point in the storyline since everything else we've learned so far have come from the secrets of other characters and we don't necessarily know if they are true or not which would make sense considering the people we have met are pretty crazy on the outside as well. Honestly I can't tell if he is being humble or arrogant but I do know that he has a point with what he said, the only person we truly understand is Nick.