The Anatomy of a Lie

 '[correcting a lie is] like putting toothpaste back in the tube, except the toothpaste is alive and didn't like the tube.'
--Tom Philips

Lies and misconceptions abound in Fictionland, just as they do in the real world. However, with the exception of a few stories which use propaganda as a plot point, most of these lies seem easily corrected once people realise the main characters were right all along. One of the exceptions is the Harry Potter series-- the tabloid lies which start circulating in the fourth book are fairly persistent, and continue to cause trouble as the story progresses-- and I think it's a demonstration of Rowling's skill at worldbuilding.

How fast and how far misinformation can spread in your story depends on the level of information flow in your setting. In, say, rural 19th century Japan will probably not be able to spread gossip much further than their relatives in the next village over, while the same people, were they in the 21st century and equipped with smartphones, could spread the same rumour around the globe in the time it takes to type 140 characters.

While misinformation and gossip do turn up as temporary plot points, usually to show what a meaniehead one of the villains is, I think the spread of juicy fiction presented as fact can become a more persistent feature of a fictional world. Even if it doesn't directly concern the main character, it can be part of the fabric of the setting, as the characters read newspapers or scroll through their Facebook newsfeeds or catch up with a travelling salesperson about current events. The character's process of figuring out what details about important events are true or rumor could even be a major part of the plot.