People do not evaluate the absolute value of their income, performance, achievements but are heavily influenced by comparison to others. H. L. Mencken defined a wealthy man as one "who earns $100 more a year than his wife's sister's husband.
Peer pressure is a strange thing. We all remember it in school. It continues throughout life. Keeping up with the Jones is the famous term. Gary McClimans once said "We are all tribal - we want to be in a tribe". It is the human condition and it starts with the family - everyone first belongs to a family, then the extended family and it proceeds from there into social networks - memberships, political parties, religious denominations, alumni clubs, Vistage, Social Venture Partners, IH Swim Club, country clubs .............
The greatest correlation they have found for happiness is human relationships. And with those relationships comes social networks and relativism.
So happiness is relative - or is it about your specific relative :)