A couple of days after Will Smith slapped Chris Rock at the Oscars, a guy you’ve never heard of who thought that Rock should apologize for having made a joke at Jada Pinkett Smith’s expense sat down and wrote out the apology that he thought Rock should give. Then he posted it to his Facebook page.

Although the apology was written as if it came from Chris Rock, the guy who wrote it was not trying to impersonate Rock or pretend that the statement came from him. In fact, his next post said something like, “That’s what I’d say, anyway.” But for whatever reason, the post started to get attention from other Facebook users. That, at some point, made Facebook’s algorithms kick in and elevate it, and soon enough the statement made the leap to other social-media sites, most notably Instagram and Twitter, where it was picked up and retweeted by users with massive followings.

Somewhere in that process, though, something interesting happened: people started to think, and to say, that Chris Rock had actually made this apology that some random guy on Facebook had written. And it wasn’t until Rock’s publicist quashed the story, confirming that the apology was fake, that people realized they’d been duped (or duped themselves, depending on your perspective).

Now, from one angle you could say, “Just another day on Twitter.” But the fact that in a matter of hours, hundreds of thousands of people came to think a completely bogus statement was true speaks volumes about how easily misinformation can spread via social media, even when no one is trying especially hard to make that happen. In this case, after all, there was no army of Russian bots trying to get people to believe that Chris Rock had apologized. It was more like an organic case of collective stupidity on social media.

Much of this was the product, obviously, of the way social media works — it’s built on the idea of influence and trend-following, which means that it wants its users to take their cues from others and from what others are doing. So if trusted high-profile accounts are retweeting something, their followers are going to assume it’s true and are going to then like and retweet it themselves. That easily creates what economists call information cascades, where the decisions of early users (in this case, the decision to treat the apology as if it was real) end up having an inordinate impact on the decisions of those who come after them.

Yet even with all that, what remains striking to me about this story is that so many people — including people with tons of followers, who you might think would have some incentive to be accurate — clearly just post and retweet stuff without bothering to make even a cursory attempt to check that it’s accurate. And they do this even when, as in this case, there are plenty of red flags. The fake apology was not posted on Rock’s official social-media accounts or his website. It spelled “making light” as “making lite.” It had Rock referring to himself as a “renown comedian,” and the tone was so abject (it said telling the joke cost him “the enormous price of my reputation as a renown comedian”) that it seemed utterly improbable Rock had written it. But none of that mattered to the people blithely posting the statement.

So what explains this (other than the fact that people are lazy)? In this case, some of people’s lack of interest in checking to make sure the statement was real was the product of their desire to have Rock apologize (something that lots of people want him to do). In other words, they saw something they wanted to see, and weren’t really interested in the possibility that it wasn’t true.

There’s also, though, something simpler at work, and that is that for most of us, our default assumption when confronted with something someone has said or written is that it’s true. You might think that we would be naturally skeptical, especially when it comes to social media. But in fact, according to what the social psychologist Timothy Levine calls “truth default theory,” most of us typically assume that what we’re told is true, and we only change our mind when we find convincing evidence that it’s not. And that assumption is all the harder to challenge when what we’re being told is something we want to hear. (Confirmation bias is a hard thing to resist.)

Levine argues that the fact that we default to assuming truth is actually a good thing, since most people are mostly honest, and it would therefore be a mistake, and quite time-consuming, to evaluate every statement as if people were lying to you. (To be sure, there are certain businesses where it would be a mistake to not assume that.) The problem is, of course, that people lie on the Internet all the time. Or sometimes they just post misleading stuff that they don’t even know is misleading. Either way, defaulting to truth leaves a lot of people ill-equipped to deal with either of those realities. Which is why the mantra of any social-media user should be that old Ronald Reagan line about arms-control treaties with the Soviets: “Trust, but verify.”