"A lie can run round the world before the truth has got its boots on."
                                                      -- Terry Pratchett, The Truth
"Real stupidity beats artificial intelligence every time."
                                              -- Terry Pratchett, Hogfather
It is my experience that stupidity takes a lot of effort to correct, and lies take a lot of time to debunk. (See this post. Lies, untruths and falsehood are easy to make and takes a lot of time to debunk.)

You would think that it should be easy to show facts and prove truth. It's not. Just try explaining to a stupid person (you can pretend that you are that person if you can't find a truly stupid person) that the earth revolves around the sun and not the other way. The stupid person just needs to tell you that that is not what his eyes tell him. Intelligence sometimes require you to not trust your senses.

It takes time to overcome stupidity (and their senses) and of course stupid people don't believe they are stupid or wrong and will resist.

It is not my job to teach stupid people to not be stupid. My interest is to learn and to improve myself.

But worse that stupid people are people who think that they are logical and intelligent. And they try to use Logic on you.

But the worst would be people of conviction:

"Convictions are more dangerous enemies of Truth than Lies" - Friedrich Nietzsche.