David Robson in The Guardian:
Over the past 10 years, numerous studies have shown that our obsession with happiness and high personal confidence may be making us less content with our lives, and less effective at reaching our actual goals. Indeed, we may often be happier when we stop focusing on happiness altogether.
Let’s first consider the counterintuitive ways that the conscious pursuit of happiness can influence our mood, starting with a study by Iris Mauss at the University of California, Berkeley. The participants were first asked to rate how much they agreed with a series of statements such as: “I value things in life only to the extent that they influence my personal happiness” and “I am concerned about my happiness even when I feel happy”. The people who scored highly should have been seizing each day for its last drop of joy, yet Mauss found they tended to be less satisfied with their everyday lives, and were more likely to have depressive symptoms even in times of relatively low stress.
Various factors may have caused that link, of course, but a second study suggested a strong causal connection.