But one of the main reasons why Denmark does so well in international happiness surveys is the welfare state, as it reduces uncertainty, worries and stress in the population. You can say that Denmark is the happiest country in the world or you can say that Denmark is the least unhappy country in the world. The welfare state is really good (not perfect, but good) at reducing extreme unhappiness. Universal and free health care, free university education and relatively generous unemployment benefits go a long way towards reducing unhappiness.
Meik Wiking, The Little Book of Hygge: The Danish Way to Live Well