Intersexual dating sights
Income is even less important as a determinant of emotional happiness.
Winning the lottery is a happy event, but the elation does not last.
Paraplegics are often unhappy, but they are not unhappy all the time because they spend most of the time experiencing and thinking about other things than their disability.
When we think of what it is like to be a paraplegic, or blind, or a lottery winner, or a resident of California we focus on the distinctive aspects of each of these conditions.
The mismatch in the allocation of attention between thinking about a life condition and actually living it is the cause of the focusing illusion. When people are induced to believe that they "must have" a good, they greatly exaggerate the difference that the good will make to the quality of their life.
That's probably part of the story, but let's be optimistic and concentrate on something remediable: lack of training in how to think critically, and how to discount personal opinion, prejudice and anecdote, in favour of evidence.
I believe that the double-blind control experiment does double duty. It also has educational, didactic value in teaching people how to think critically.