You probably know some of those people — yeah, exactly those — who are sure their and only their opinion about, their explanation for or their belief in something is true is and cannot be persuaded, even if presented with overwhelming evidence to the contrary, that they might be wrong on this matter.
How can those people ignore evidence, arguments, pleading? Why are they that stupid? Are they evil demons plotting to destroy the world with their ignorance?
Now take a step back and think about all the things you know — beyond the shadow of a doubt, with utter certainty — to be absolutely true.
We're morons, every single one of us.