Which is what the article says in the abstract: "We argue that this pessimistic bias stems from the fact that trendsetters and socialites come most easily to mi

Which is what the article says in the abstract: "We argue that this pessimistic bias stems from the fact that trendsetters and socialites come most easily to mind as a standard of comparison and show that reducing the availability of extremely social people eliminates this bias." There's also the well-known effect of social media where you see everybody's highlights and best moments, but unless you're close you won't hear about the boring or unhappy parts of their lives. I don't think the article tackles that though.