So for instance if you're Scandinavian you're expected to say you're happy. This is pretty much one of the first things everyone says when it comes to the region. And if you haven't thought too much about it lately, perhaps you are inclined to just tell the researcher a stock answer.
How do we know that people are not just saying what is expected of them? I think there's at least some evidence that people tend to do that when asked a question.