Nationalism & Identity
Norwegians define themselves in simple terms: they are not Swedish. This simple definition comes from centuries of being dominated both politically and culturally by the Swedes, and millions of foreigners believing Norway to be the capital of Sweden (it's not, just in case you are unsure).
To show the world that they are Norwegian and definitely not Swedish, every Norwegian, at any moment in time, will be wearing an item of clothing with a Norwegian flag on it.