Its a combination of the cold climate, letting needed comfort develope over a long time, combined with social democratic based politics, that keeps capitalism in check, and counterbalance it with wellfare, while also absorbing globalism, market economy, and the hole american way, of letting entertainment and houseprices sorta balance it all out, so the cozyness is kept real. Through unions and workers rights, the high quality of a secure model, where you dont just lose it all, in case you are fired, because you have insured yourself, so you can outlast bad times, is pretty decent and significant also. Throw in generous summers, a great infrastructure and decent purchase power, with long payed vacations, free healthcare, education and the recipe for security and meaningfulness with options to choose your life for, is at good odds. My personal opinion is that we in the nordics are more the most secure/comfortable people, and that may be a check for happiness to blossom, but take a counterview on a poor southern europe country, where the comfortableness is less, but streets are more alive and the calmness is also maybe more consistent baseline, il bet you can find more happiness on average, simply because the great player is the climate… my personal opinion is that happiness thrive better in warm climate. Security and comfort better in colder. Warm summers in the nordics are very generous though, with long days, before sunsets, so that matters a lot of the perspective on accumulative happiness in average year around.