This NY Times article explains why it’s so easy to believe information that is demonstrably false. Part of the reason is that much of what we know is actually “collective” knowledge.
“Knowledge isn’t in my head or in your head. Consider some simple examples. You know that the earth revolves around the sun. But can you rehearse the astronomical observations and calculations that led to that conclusion? You know that smoking causes cancer. But can you articulate what smoke does to our cells, how cancers form and why some kinds of smoke are more dangerous than others? We’re guessing no. Most of what you “know” — most of what anyone knows — about any topic is a placeholder for information stored elsewhere, in a long-forgotten textbook or in some expert’s head. It’s shared. One consequence of the fact that knowledge is distributed this way is that being part of a community of knowledge can make people feel as if they understand things they don’t.
The key point here is not that people are irrational; it’s that this irrationality comes from a very rational place. People fail to distinguish what they know from what others know because it is often impossible to draw sharp boundaries between what knowledge resides in our heads and what resides elsewhere.”