Dan Hannan explains in a Washington Examiner column why optimists face an uphill political battle.

Given the circumstances of its founding, you’d think America would be an optimistic, forward-looking place. Yet according to Pew Research, most Americans believe that life was better 50 years ago.

True, the margin is not huge: 41 percent to 37 percent. Even so, what an astonishing finding.

I wasn’t yet born then, but here are a couple of things I know about 1968: There were no cellphones; color TV was a luxury; and jet travel was for the rich. …

… How can Americans be nostalgic for such a time? How can anyone? Yet they are.

Nigerians pine, by 54 to 41 percent, for 1968, the year their country was convulsed in the Biafran war and their people had a life expectancy of 41 years.

Peruvians long — 46 to 29 percent — for the year that Juan Velasco launched his baleful military coup, plunging their nation into years of poverty. Thirty-nine percent of Hungarians pine for the days of János Kádár’s dictatorship, and only 32 percent think things are better today. …

… [A] team of Harvard researchers has shown why our brains are configured to be gloomy. It turns out that as a problem gets smaller, we tend to exaggerate what’s left of it. Asked to identify angry faces, for example, respondents began to glimpse them more frequently as they became rarer, reclassifying expressions that they had previously called neutral. Similarly, when unacceptable remarks became rarer, they began to find fault with remarks that they had previously categorized as inoffensive.

The Harvard team gives this trait the ungainly name “prevalence-induced concept change,” and it’s the key to understanding politics. As long as people are temperamentally unable to accept that things are getting better, they will be drawn to candidates who, for example, tell them that crime in America is rising (it’s falling), that immigration is out of control (in 2015, for the first time, more Mexicans crossed the border southward than northward) and that ordinary Americans are getting poorer (they’re getting richer).