The Danes are the world's most trusting people. Historians and researchers believe that the Danes' nature of trusting other people goes back to the time of the Vikings. The Vikings' domestic economy was simply built on trust: If you live in a time with no police or courts, and you entrust some animal furs to a trader, you need to be able to trust that trader to pay you your money once he returns - often months or years later - from his trade trip.
Trust is very important for the economy to function. According to some researchers, a "10 percent negative change in the level of trust in a population will cause a half percent negative change in economic growth." Both Vikings and anybody who has ever borrowed or lent money knows that trust is important when it comes to finances. Without trust, there will be either no deal or a lot of resources will need to be invested in insurance, lawyers and bureaucracy.
Trust is also believed to be a prerequisite for happiness (Trust Hormone Associated With Happiness, Happiness flows from trust - etc.). Trust increases the feeling of security, and feeling secure is - unless you are looking for certain types of excitement - a necessity for feeling happy. No wonder the most trusting people are also the happiest.