The key to happiness is low expectations

From an article offering possible explanations why Denmark has yet again been ranked as the world's happiest country:

In 2006, researchers from the Institute of Public Health at the University of Southern Denmark examined a range of possible factors, from genes to cycling habits to cuisine. In a charming report, they offered two explanations: the Danes have never got over their rapture at winning the European football championships in 1992 (their happiness rose to new peaks that year, and has stayed on a plateau since), and—the main finding—Danes, unlike the woeful Greeks and Italians, have very low expectations of the immediate future. "Year after year," the researchers write, "they are pleasantly surprised to find that not everything is getting more rotten in the state of Denmark."

- Sally Laird, 'Why Hamlet's Heirs Are Happy', Prospect Magazine, September 2008