People That Hold Irrefutable Beliefs: Are They Just Mouthpieces Of Their Belief?

Some people are absolutely certain of their belief. Absolute. Irrefutable. No doubt whatsoever. The position from where they speak is: “I know, you don’t. Here are some facts that prove that I’m right. You should do it this way, because according to my facts, they’re the right way to do it.” They surround themselves with people and news outlet that confirms their belief; they cherry-pick data that supports their belief. When they’re presented with data or information that completely disproves their belief, they change topic, or worse, they lash out. Do they know what they’re talking about, or are they merely a mouthpiece of the belief?