Nick has certain advantages which are explained in Chapter 1, particularly, his ability to be involved in the shallow, fast paced lifestyle of Gatsby and the others, while maintaining his moral center.
Nick is attracted to the rich and glamorous ways of the other characters, but he is more realistic about life.
"In keeping with Nick's code of conduct, inherited from his father, we learn from the very beginning of the novel that he is “inclined to reserve all judgments” about people because whenever he feels compelled to criticize someone he remembers “that all the people in this world haven't had the advantages that you've had.”
"At first the reader might think the advantages he alludes to are monetary, but then Nick acknowledges that he agrees with his father: “A sense of the fundamental decencies is parcelled out unequally at birth.” Clearly, decency, not wealth, is the supreme value."
Nick's father tells him,"a sense of the fundamental decencies is parcelled out unequally at birth." Some of Nick's "unequal" advantages are:
1. Family background: "My family have been prominent, well-to-do people in this middle-western city for three generations."
2. Education: Both his father and he graduated from one of the most prestigious universities in America-Yale University in New Haven.
3. Financial freedom: Since his father looks after the lucrative family wholesale hardware business Nick is free "to go east and learn the bond business."
4. Luxurious and independent lifestyle: Nick has the money to rent an entire house for himself after his co-tenant is transferred to Washington. A Finnish housekeeper looks after the house and does the cooking. He has his own car and he buys up many books about the "bond business" but is in no hurry to learn the business.
All these "advantages" which his father keeps reminding him of frequently, have made Nick to be tolerant of others' shortcomings and more importantly a sympathetic and non-judgemental listener. It is this second quality which attracts Gatsby to Nick and persuades him to reveal the truth about his antecedents and shady past in Ch.6: "James Gatz-that was really or at least legally his name............the vague contour of Jay Gatsby had filled out to the substantiality of a man. He told me all this very much later."