Eric Tucker, a 35-year-old co-founder of a marketing company in Austin, Tex., had just about 40 Twitter followers. But his recent tweet about paid protesters being bused to demonstrations against President-elect Donald J. Trump fueled a nationwide conspiracy theory — one that Mr. Trump joined in promoting.

Mr. Tucker's post was shared at least 16,000 times on Twitter and more than 350,000 times on Facebook. The problem is that Mr. Tucker got it wrong. There were no such buses packed with paid protesters.

But that didn't matter.

While some fake news is produced purposefully by teenagers in the Balkans or entrepreneurs in the United States seeking to make money from advertising, false information can also arise from misinformed social media posts by regular people that are seized on and spread through a hyperpartisan blogosphere.

Here, The New York Times deconstructs how Mr. Tucker’s now-deleted declaration on Twitter the night after the election turned into a fake-news phenomenon. It is an example of how, in an ever-connected world where speed often takes precedence over truth, an observation by a private citizen can quickly become a talking point, even as it is being proved false.