The current debate on “fake news” keeps turning my thoughts back to a moment in China 40 years ago.

It was May 1977, eight months after Mao Zedong’s death. China’s new leaders were just beginning to assume control. The great policy changes that would so stunningly transform the Chinese economy and ideology had not yet begun, so the country I was seeing for the first time was still essentially Mao’s China — unimaginably different from the China of 2017.

I had been writing about Chinese affairs for several years from Hong Kong, then still under British rule. But that trip in 1977 — on a six-day journalist’s visa to visit Guangzhou, which foreigners then still commonly called Canton — was the first time I was able to get a first-hand look.

On one of those days my escorts took me on a tour of the Guangzhou Heavy Machinery Plant, where some 5,800 workers turned out equipment for oil refineries, chemical and metallurgical factories, and other industrial facilities.

The factory walls were plastered with posters celebrating Mao and the new party chairman, Hua Guofeng, and pledging redoubled efforts to carry out “Chairman Mao’s revolutionary line.” But the scene on the factory floor looked nothing at all like heroic revolutionary struggle. Only a few workers were actually tending machines. Most were standing around lackadaisically, sipping tea and chatting with each other or reading newspapers.

I was quite startled — and then even more startled when it dawned on me why I found the scene so surprising.

Unconsciously, I realized, I had expected to see something resembling the posters and photos I had seen for years in Chinese publications, images of workers straining every muscle and with exalted expressions on their faces as they gave their all to build China’s socialist dream.

What was startling was not learning that the propaganda images were untrue. What jolted me was how much they had influenced me even though I knew they were false.

Only months earlier, the same publications that regularly showed those heroic workers had published openly doctored photographs of Mao’s funeral. Blurred smudges showed where Mao’s now-vilified widow, Jiang Qing, and the other members of her Gang of Four had been crudely airbrushed out of the scene, while rows of small x’s covered over their blotted-out names in the captions.   

Remembering those photographs and countless other falsehoods, I would have said with completely certainty before that day in the machine factory that I knew Chinese propaganda for what it was, and would never confuse its false messages with reality.

But here I was, standing on a factory catwalk and looking out over all those workers standing around drinking their tea, and realizing that I was not as immune as I thought. Even knowing how unreal those propaganda images were, I still carried them in my mind as picturing what I would see in a real Chinese factory — and was shocked when the reality turned out to be so different.

The lesson from that day has stayed with me: false information has power on a level below conscious thought. When it’s vivid enough and comes at you often enough, it can strongly influence even people who know it’s wrong. And in today’s landscape, where information has a presence and reach light-years beyond what Chinese propagandists or anyone else could imagine 40 years ago, the power of untruth can be very troubling.

Just consider this country’s political debates of the last year, and the completely contradictory versions of reality that emerge in every day’s political news (or every hour’s). What effect has that discourse had on the public mind?

Or, to set partisan matters aside and consider a story that everyone agrees was false, ask yourself what might be the lingering residue of the false Rolling Stone article on an alleged rape at a University of Virginia fraternity house? Even after people knew it was fabricated, did that story nonetheless still leave many with a sharper impression of UVA fraternities, and fraternities in general, as hotbeds of sexual assault? 

What about the claim that a Muslim conspiracy to impose sharia law on the United States is a significant threat to America’s legal system? Does that story heighten suspicion and fear of Muslims even among Americans who have enough common sense to understand how preposterous it is?

(As one Muslim American pointed out to me, in a majority Christian country where advocates of “Christian values” have not been able to bring back a ban on abortion or restore prayers in the classroom or block legalization of gay marriage, the idea that Muslims, with somewhere between 1 and 2 percent of the population, can subvert and capture the American legal system is clearly delusional.)

Or think about the national debate over policing in minority communities. Do the competing shouts of “cops-are-always-guilty” and “cops-are-never-wrong” raise the levels of distrust and fear even among those who realize that the facts in police shootings are not only different in every case, but also typically more ambiguous than clear-cut?

None of those are quite as blatant as the Chinese propaganda I remember from four decades ago (although the sharia story comes pretty close). And this is not even to mention political attack ads and the increasingly toxic tidal wave of three- and four-Pinocchio lies and distortions that roll over us every election season.

On that long-ago day in Guangzhou, beside knowing that Chinese propaganda did not represent reality, I also knew plenty of other reasons why I shouldn’t have been  surprised to see those idle workers on that factory floor.

It’s hard to remember now how far behind China was at the time, but the Chinese economy in 1977 was about one-twelfth the size of America’s, as measured by gross domestic product, in a country with more than four times the U.S. population, an official policy of 100 percent employment, and a socialist economic system with no profit motive. In those circumstances, overstaffing on a vast scale was inevitable.

I knew that, so logic, too, should have led me to expect what I saw, instead of being surprised by it. But it didn’t. It was sobering 40 years ago in a Communist dictatorship on the far side of the world to realize how powerful a lie can be even when you think you know better. In my own democratic country today, for many reasons, that thought feels even more sobering.