“It’s about chasing the viral dragon,” said Matt Waite, a professor of journalism at the University of Nebraska and developer of PolitiFact, a fact-checking website.
“If you wait for facts to ruin a good story [by showing the story is not true], then you won’t be in on the pageview bonanza, and your bosses want to be in on the pageview bonanza,” Waite added. “So, post goes up, facts come later.”

Source: The left’s emerging ‘fake news’ problem
“Fake news” is a term initially applied to purported news reports that tweak the emotions of (mostly) right wing conservatives, who then share the stories online, causing the “fake news” to reach millions. As many outlets, including this blog, have documented, much “fake news” comes from both the right and the left – and from mainstream news sources.
Today, every news outlet tracks readership and viewers. That data is mined for insights on how to create news reports that attract more readers and viewers’ eyeballs for advertisers. They track everything and you won’t believe what happened next!
Everyone is learning from the viral fake news success and adopting those techniques even at mainstream news outlets.
“Fake news”, broadly defined, includes

• Satirical “news reports” that are intended as humor (think of The Onion) but which are often shared as if they were actual news reports.
• “News reports” written with a bias or based on an ideological perspective. Many news reports, not generally labeled as “fake news” might come from ideological news sources such as Fox News or MSNBC, and other traditional news outlets. A related group are news aggregators which link to a biased selection of news reports, such as the Drudge Report.
• News reports that contain exclusively accurate information but are fake by virtue of leaving out critical information. This is known as an “error of omission” (versus an “error of commission”). Biased news reports often use this approach because the reader or viewer assumes “what you see is all there is” and is not aware of conflicting information. This method is often used by mainstream news outlets.
• “Fake news” written specifically to inflame emotions, to encourage sharing on social media for the purpose of driving eyeballs to advertisers.
• Many well known “fake news” sources are for profit, online-based, social media centric publishers whose goal is not ideology but advertising profit. They use methods and propaganda to target the emotions of their audience to encourage viral sharing that drives eyeballs to advertisers. There are right wing fake news sources produced by liberals and left wing fake news sources produced by conservatives. It’s all about the money and has little to do with ideology – its just a business.
• Some times, “fake news” sources produce true stories, together with fake and exaggerated stories, making the classification of “fake news” difficult.
• Fake news can contain entirely accurate information yet by leaving out crucial details, is effectively a fake news report. This is why classifying news as fake or true can be challenging.
• Fake news tends to rely on emotional hooks, is often poorly sourced, is uncorroborated, leaves out crucial information, and is widely shared on social media.
• Fake news can and does originate from satirical “news” web sites, from online, social media based for profit “emotionally laden” (especially political) publishers, from ideological and propaganda-oriented organizations (including non-profits, government agencies, universities and businesses), and from traditional mainstream news services. These organizations often use methods of propaganda (also known as persuasion) to try and convince others to adopt someone else’s agenda and may use false stories or stories containing both true and false elements, to reach their targets.

There is a difference between deliberate fake news and making a mistake or error in reporting. Mistakes happen all the time, although, based on my own experience with news stories about topics or events in which I am familiar, are rarely corrected. However, the difference is that mistakes are not the same as deliberate and intentional misreporting. A story with an error is not necessarily “fake news”; but a story that deliberately and intentionally misreports is “fake news”.