Most people wouldn't share something they suspected to be untrue, so it's probably safe to posit that a fake rumor is more likely to be successful if it makes someone say, "yeah, sure, makes sense to me!" Unfortunately, we have a hard-wired tendency to try to fit every new piece of information we learn into what we already know to be true. This can lead us to dismiss evidence of climate change as being obviously untrue, or encourage us to cherry-pick pieces of data that support the (debunked) notion that global warming is happening naturally, without human input. Our brains are desperate for evidence that what we already believe is true, which makes it oh-so-tempting to take for granted something that fits our favorite narrative. Admit it, it's happened to you: even if you're sure you're not one of those people who spreads so-called fake news, it's pretty dang likely you've accidentally shared something false at least once because something in your brain sang out "yessssss, I knew it."